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Research Guide for DAsH (or digital humanities) resources and tools

Historical Map Resources

Georeferencing is a tool in ArcGIS pro that allows you to take a map that is an image file and add geospatial data to it so that features on that map (lakes, streets, buildings) sit on the map canvas in the accurate place. This is useful for maps created by agencies for use in display that don't have GIS data attached to them if you want to see where your data lies on it. For example, if you wanted to use flood plain data to compare to census data, but the only flood plain map you can find is just a jpeg, you can georeference that map using ArcGIS Pro's tools and it will then be usable just like any other kind of GIS data.  

Also ,if you are working on something for a history project and you want to use a historically accurate map for the area you are looking at, you can use some of the resources above to be able to find a map that is accurate to the place and time you need a map for.

Notes on Historical Maps

It's important to remember that place names change over time, so if you are trying to map things within a certain era, you are best off finding a historical map to confirm that if you are trying to map a writer's residence at 15 Elm Street in 1935 that the Elm Street on a current map is the same as the one in 1935.

Learning Goals

Non-georeferenced maps may still be be items you want to use in a project. Maybe you are using a map in a history project and want to understand how parcels of land have changed over time, and tell you something about your subjects' lives. Maybe you are interested in environmental studies and you want to layer satellite images that show deforestation to track how those changes have influenced the demographics of a region. Even if you have found a map that doesn't have GIS information, you can take an additional step to add those values to the map by georeferencing it. 

Georeferencing is the process of taking what is called a raster (as opposed to vector) image and positioning it into geographic space. A raster image can be many different kinds of drawings or photography including satellite imagery, architectural drawings, or in the case we'll be exploring here, a scan of an old map. When this is georeferenced, geographic information such as coordinates is added, so that by adding features to the map, for example, if you wanted to mark where certain buildings that were meaningful to your project were, you are placing them as a specific point on the globe that you can relate to other map points or layers. 

With this tutorial you'll take a historical map showing how Marble Hill used to be connected to Manhattan before the Spuyten Duyvil creek was extended to allow for easier shipping. I've placed the map below but it's also available in the New York Public Library's Digital Collections.


Getting Started

  • Download OldMarbleHIll.jpg and save it to either a folder that you have already connected to ArcGIS via the Catalog pane or one you can easily navigate to do so. 
  • Take a look at the image and take note the street names to see where in New York is covered by the map, so you know where to navigate to when you open the map. You can compare it to the current Marble Hill area in Open Street Map or Google Maps to get an idea of what the area looks like today. 
  • When ArcGIS Pro opens, in the New section of the window that opens choose Map under Blank Templates.
  • Create a New Project window will open, let's name this project OldMarbleHill You can also choose where it will save this project to. By default, mine goes to a Projects folder where I have ArcGIS saved on my computer, but you may decide to save it somewhere different. Wherever you save it to, take note of where it is on your computer. You will need to navigate back to it at the end of this tutorial so that you can zip the project folder along with all the other files that you have used.
  • Since for this map we'll only care about where streets intersect (i.e., not topography or elevation) let's use the Basemap dropdown to change the map type to Streets.
  • In the Catalog, right-click on Folders and choose 'Add Folder Connection'. Maneuver to the folder that you have put the OldMarbleHill file in and click OK.
  • Right-click on OldMarbleHill in that folder and choose Copy.
  • Scroll back up to the folder created for this project in the Catalog pane, which will have a little home icon atop it, OldMarbleHill. Right-click and choose Paste. Make sure that this is the layer that you add to the map, not the one in your original folder. In fact, right-click on the folder you added and choose Remove so the only folder that's in your catalog is OldMarbleHill
 ArcGIS Pro is very picky about file structure and if you do not keep a consistent file structure, then any layers, files, shapefiles, selections, or any other modifications that rely on being able to access those files, layers, shapefiles, tables, etc, change then your project file will be defunct and all those layers will need to be added again, and any joins or other modifications will need to be redone. 
  • Use the Navigate and Map tools to get to the area of the map that you'll eventually be mapping, the neighborhoods of Inwood and Kings Bridge (228th street down to about 207th). Put in a bookmark here so you can get back to it easily. Go to Bookmarks under Map in the toolbar and choose New Bookmark.
  • Name the bookmark Marble Hill Full and save it. 
  • Go to the Catalog window. Click on OldMarbleHill.jpg.  It should have an icon that looks like a grid next to it. Drag it onto your canvas.
  • You'll get a request to Calculate statistics for OldMarbleHill.jpg, choose Yes.  
  • It will calculate, and then there will be a warning, saying that the data source is missing spatial reference information so it cannot be projected. We already know that it is lacking this information, and that's what we will handle when we georeference it, so ignore this warning. 
  • Your Contents pane will display OldMarbleHill.jpg as a layer, but the display on your canvas won't change. To see where ArcGIS decided to place the image, right-click on OldMarbleHill.jpg in the Contents pane and choose Zoom to Layer. You'll see that it's placed it way out over the equator.
  • Access the Marble Hill Full bookmark that you've created by clicking on the Bookmarks dropdown and selecting itIt'll take you back to the section of the map that you intend to place this new map on. 

Preparing to Georeference

You add georeferencing by adding control points to a layer and to the map beneath it at the points where the two share a common street intersection, building, mountain peak, whatever is easy to identify on the map layer you want to georeference and on the base map below it. When you add enough of these, ArcGIS will be able to rectify the two items, and accurately stretch and place your map layer over the locations on the basemap that it covers. 

  • Click on Imagery in the menu bar and choose Georeference. This opens a new set of tools. 
  • To get started, choose Fit to Display and the map you're attempting to georeference will fit itself across the center of the frame.

There are two methods for being able to see beneath the OldMarbleHill layer onto the basemap. One is to just use the checkbox next to it in the contents pane to turn it visible and not visible. The other is to go the Appearances tab under Raster Layer and using the bar next to Transparency to set the layer to be more transparent.

I prefer to check and uncheck visibility for OldMarbleHill.jpg in the Contents pane, since to place the other half of an anchor point  I'll have to be moving between the OldMarbleHill.jpg layer and the basemap anyway, so that's how I'll be explaining it. 

  • You'll next be choosing control points that exist on both maps. Think of it as you are telling ArcGIS Pro which points have to be on top of each other so it can pull the rest of the map in place around it, like you are sewing two pieces of cloth together. 
  • Let's switch back and forth between the two and identify 4 intersections or features that exist on both. This is a little challenging since obviously, the reason for creating this map is so because we want to see how the coastline changed, but fortunately there seem to be some consistencies.
  • Starting from the bottom left, it seems that the intersection between Isham and 10th is on both maps. When we've located it, create a bookmark over it, by making sure you have World Street Map highlighted in the Contents Pane,  going to Map, choosing Bookmarks, New Bookmarks and naming it Isham and 10th
  • Farther down and towards the center, we can also see that the intersection between Vermilye Ave and Dyckman Street is on both maps, even though the spelling of Vermilyea seems to have changed to include an 'a'. Put a bookmark over it on the base map called  Vermilye Ave and Dyckman Street
  • In the top left, we have 218th Street  intersecting with Seaman Avenue on both the OldMarbleHill.jpg map layer, and on the basemap layer. Put in a bookmark for this spot on the basemap called Seaman Ave and 218th Street.
  • Lastly, before we start actually putting in these control points, let's find a fourth point.  In the top right 220th Street and 9th Avenue intersect on both maps. Let's put a bookmark there called 220th Street and 9th Avenue

Now that you have the first four points picked out and bookmarked you are ready to start adding them as Anchor Points. The reason for the bookmarking is because every time you add an anchor point, your map will shift, and this will just make it easier for you to get back to each of those points as the map shifts. 

Adding Anchor Points

  • Let's start with the first point we picked, Isham Avenue and 10th Avenue. Turn the visibility on for OldMarbleHill.jpg on, and select that layer. Use the Explore tools on the Map tab to zoom and pan over to that location. 
  • Click back into the Georeference tab and choose Add Control Points. Your cursor will change to be a little cross, and when you hover there will be a little bit of text that says From point (source). Click on the northwest corner of the intersection between Isham Avenue and Tenth Avenue on the map.
  • The cursor will change to say Endpoint and put a little red square at that intersection. Uncheck the visibility on OldMarbleHill and if you need to find the intersection on the World Street Map, use the bookmark for Isham and 10th. It looks like when I used  Fit to Layer it placed these close enough together, so I won't need it. The cursor will now say To Point (target). So I'll click on the northwest corner of the intersection between Isham (now street) and 10th Avenue on this map, and it'll change to be a little red circle with a cross through it. 
  • Use the Explore tools under Map to get out of the mode where you are adding a control point, and find your way back over to where Dyckman Street and Vermilye Avenue intersect on the OldMarbleHill.jpg map layer. Click back to the Georeference tab and choose Add Control Points. Click on the top right corner of that intersection first on the Old MarbleHilll.jpg layer, and then on the basemap, and the map will shift again. 
  • Next, it'll probably be easier for us to get to our third point, by using the bookmark for Seaman and 218th Street, and then using the Explore tools under Map to get to the place on the OldMarbleHill.jpg layer where 218th and Seaman intersect. I'll put the anchor point on the bottom right of the intersection, which is admittedly a little tricky since on this 1879 map the 218th street was still theoretical, but I'll approximate it the best I can. Next, I'll place the other half of the anchor point where the bottom right of the intersection is on the two streets on the modern base map, using the bookmark to get back to it if I have any trouble finding it. 
  • Let's add the last of the control points we had planned, 220th Street and 9th Avenue. Use the bookmark to get back to it if you need to. Put a control point on the top left corner of the intersection on OldMarbleHill.jpg and on the base map underneath it.
  • If you make any mistakes or want to delete a control point, you just need to choose the Control Point Table option on the Georeference tab. You can delete a point using the icon with the little red x next to it, and if you want to check and see how the map changes if you get rid of a particular control point you can just unclick the box next to it. 

Zoom out and either adjust the transparency or turn the OldMarbleHill.jpg layer off and on to see how the maps are lining up. It looks like we might need to make some adjustments on the left-hand side of the map, which we can do in the next step by adding additional control points, and by configuring the Transformation of the map. 

Fine-tuning with Transformations and Added Control Points

The Transformation tool controls the method that ArcGIS is using as it figures out how to fit the map layer you're georeferencing around the Control Points that you've added to it. The more points you have, the closer it can get to fitting the two maps together. Let's see what happens when we change what transformation we are using. 

  • Click on Transformation to see the options available. By default, my map is transformed using 1st Order Polynomial. There seem to be a lot of other options. Some are greyed out, and the additional information below them gives a clue why. Each of them needs a certain number of control points to work. Currently we have four, so some just aren't available to us. 
  • Let's switch to some of the others that we have enough control points for, by clicking on them.
    • Projective clearly doesn't work with the control points that we currently have as it extends the map out widely, so we'll want to add more control points towards the top of the map if we want to use that one. 
    • Adjust looks pretty promising actually, as we click OldMarbleHall.jpg in and out of visibility, or use the transparency option if that is preferred. 
    • Similarity Polynomial also looks promising, and for now, let's stick with that one as we see if there is anywhere else that we can add control points. 
  • Scroll down to the bottom left of the OldMarbleHill.jpg map, and turn its visibility off and on to confirm a hunch. It appears that what was Inwood St on the 1879 map, is now a continuation of Dyckman St. In this case, I've done some further research in the NYPL's online map archives and confirmed that is the case. So let's add another control point where what's Inwood St on the OldMarbleHill.jpg map and Dyckman St on our modern map intersect with the railroad track.
  • Choose Add Control Point and add a point where Inwood St ends before the railroad track on OldMarbleHill.jpg and create the second half of it where Dyckman St ends right before the railroad track
  • Zoom out and try the map trick again to see if it can tell us anything about if that control point helped anchor the map better or not. In this case, it looks like yes. Let's add one more control point on the far left of the map, and choose the only other point I can see that exists on both maps, where the railroad track reaches the very edge of the peninsula. 
  • Zoom out to see if you think that the map is laid out well. Go through the different Transformation options again to see if they match up the way that you'd like. Actually, now that the control points to the west side of the map have been added, Projective seems to provide the best match, so I'm switching it to that. 
  • Let's Save this map by clicking on the Save icon up at the top right of the Georeference tool bar. This needs to be done otherwise the jpeg that you've just spent all this time georeferencing will just remain a jpeg. 
  • To see what this change has done, open the file that you've created for this project in Windows Explorer. In addition to the jpeg file that you've added, there are now all these other XML files or other kinds of files that have the same name. If you plan on taking this jpeg that you've georeferenced and add it to a different maps, you'll have to ensure that you bring all those other files with it too. 


Adding Metadata

Whenever you add a layer with information to your map, you'll want to also add additional data about where you got that information so that your viewers will know where it came from. This data about data is called 'metadata'. 

  • Right-click on OldMarbleHill.jpg  in the Contents pane and choose Properties.  Click on Metadata.
  • Change the dropdown that says Show metadata from data source (read-only) to Layer has its own metadata
  • Return to the location where this map came from on the NYPL's website
  • Click on the tab marked Cite this Item on that site, and copy the citation style you desire into the Credits field and choose OK. This way when it comes time to add this information to your paper, you aren't scrambling for what and where it is. 

Saving Your Map

  • Click on the Project icon at the top of your menu bar and choose Save. If you are on your own laptop and don't plan on sending yourself a copy of your file to open elsewhere, you're all set. However, if you want to open this project file in another computer, or if you want to send your professor your project because it's finished or because you have a question, this is only part of what you need to do to ensure that you'll be able to access the project later. The other steps will need to occur in Windows Explorer, so exit ArcGIS Pro. 
  • Go to Windows Explorer. Navigate to the path that your project was saved to at the beginning of this lesson, and locate the folder OldMarbleHill. You've already opened it in the last step, so you know the images are there. 
  • Go back up a level to where your OldMarbleHill folder is locatedRight-click on it and choose Send to and select Compressed (zipped) folder
  • Windows will create a zip file of your project folder with your project file in it along with all the other files that it depends on. This zip file is what you will want to save to your Google Drive or flashdrive in order to access this project later if you are not just using ArcGIS Pro on your personal computer. 
  • If you had any issues creating this file, and need to see how I had it set up, here is the zip file that I made.

Learning Goals

You can further customize a map by adding your own features to it, creating your own feature class. Similar to how you may have downloaded shapefiles that depict where certain landmarks or facilities are from say, Open Data NYC, you can create your own file called a feature class where you mark with points or polygons the locations important to your research. You can store all of these items within something called a geodatabase that packages all your data for a given project together.

With this exercise, you'll create a polygon feature class showing where modern day Inwood Park is so that you can reference it on the older map to see what areas have been turned into this park. You'll also trace part of the coastline of the older map as a line feature class so that you can see what parts of the modern coastline are filled in compared to the edge of the Hudson River in Manhattan in 1879 which could be helpful from an urban-planning perspective.

We'll be picking up from the same point we left off at in the last module of the tutorial, but if you are just starting from here, the map will be available to you below to start from. 


Getting Started

  • If you are just starting from this module and don't already have a georeferenced map project file, go to wherever you have saved the above file to, extract the zipfile and open the OldMarbleHill map project file inside.
  • Take a look at the layers, there is a layer called OldMarbleHill.jpg which contains an 1879 map of this area, which when you turn its visibility off and on, you'll see that it is layered over a modern map of Marble Hill. 
  • Use the Explore tools to pan over to the top left side of the map where the Inwood area borders the Hudson River. This is where you'll be adding your line feature class. 

​Creating a Feature Class

  • Go to the Contents pane and open the Folders dropdown, then open the OldMarbleHill folder where the other files for this map stored. 
  • Right-click on the geodatabase created for this project OldMarbleHill.gdb and choose  New and Feature Class
  • It will open a Create Feature Class window. Give your feature class the Name Coastline1879 and Alias Coastline in 1879. Since we are creating a line, use the dropdown to select Line as the Feature Class Type. Uncheck the box next to Z Values as we aren't working with anything 3D. Leave the other default checked about adding the dataset to the map. Choose Next.
  • This is where you can add any extra information that you want to be part of your feature class, whether it be text or numbers. I'll add one called BodyOfWater by clicking on the bottom, and in the field that appears, adding that in the blank under Field Name. I'll leave the Data Type as Text, but you can see the other available options in the dropdown. I'm only planning on tracing the Hudson River coastline because as you'll see this is quite time-consuming, but if this was ever anything I wanted to come back to later, I might want to include that information. If I wanted to trace some of the other coastlines, I could then specify whether the coastline was from the Hudson, Spuyten Duyvil or Harlem Rivers. You can always add another field later, but this is an opportunity to at the outset when adding features, to choose what information you'll be recording about them. Choose Next.
  • The next window is regarding the coordinate system that you'll want to use for this feature class. The Create Feature Class tool has already selecting the system that our other layers are using, we won't need to change it. Choose Next. 
  • You can leave in the default for the next two windows too, it's about the distance between coordinates before they are considered equal and what the resolution is. The last window can also just be left on the default. Choose Finish and it will get to work creating your feature class. 
  • When it finishes, there will be a new item on your map labeled Coastline in 1879 but when you right-click and choose the Attribute Table you'll see that this is still blank. That's because you'll be adding the records in this table yourself as you draw this line. Exit the attribute table. 

Adding Lines to a Line Feature Class. 

  • Go to the Edit tab in the menu bar at the top and click on the icon that says Create. This will open the Create Features window in the pane to the right of the screen. 
  • Click on the name of your layer, and it will show you the options available to use to create features for this class. It will also put a toolbar down at the bottom.
  • These options are from left to right on the Create Features window
    • Line - Create Line feature, this is for straight lines
    • Right Angle Line - this is for if you are outlining lines that connect at right angles
    • Split - When you want to split an existing lines
    • Radial - Series of lines from a central point
    • Two-point line - connect two points
    • Freehand - this is what you'll mostly be using, totally freehand
    • Trace - trace an existing feature (this only works if there are features within a layer that you are on). 
  • There's are also editing features you can use on existing lines at the top
    • Merge - This take a bunch of line features and turns them into only one. We'll be using this after we trace the coastline to merge all the lines that we've drawn together
    • Edit Vertices - This tool turns your line into a group of points that you can then move about to change how the line is formed
  • Let's start using the Freehand tool. When you click on it, you'll see that the cursor changes to a little cross. Once you click, you are drawing. So before we begin drawing, we need to move to the bottom of the coastline with the Hudson that we plan on tracing.
  • Click and trace that first section of the coastline as far as you can while still following it (I get to the bottom of that little outcropping). Then double-click to get out of drawing mode.
  • If you make an error, you can delete the line you've drawn, or use Ctrl-Z to Undo. Err on the side of tracing too little at once as you'll be able to merge lines that you've drawn, but you can't delete just a portion of what you've drawn while you're in the Freehand tool, just the whole line you've drawn in that session. You can start off the next line right up against the last one and it's better if there is some overlap rather than a gap because we'll be merging these lines all together at the end. 
  • When you get to a more straight-lined portion of the tool, you can use the straight line function, that first icon on the panel. For example, when I get to around the middle of that one section of land butting out into the water, I'll use the line tool. This tool draws fully straight rather than letting you trace the curvy section of the coastline. Click to start a new line, and and it's easier to trace a coastline that contains more straight stretches.
  • When you have traced to the edge of the screen, you'll have to go back up to Map Tool and use the explore button in order to move the map. Otherwise the drawing tool will be enabled. To get back into drawing mode, we'll need to go to the Edit tab and choose the Create button again, and then select the tool we want to use to draw the line with. 
  • I'll be using a combo of the freehand tool and the line tool until I get to that little rectangular dock but you should use whichever you think is best. 
  • At that little rectangular dock there's an opportunity to try a different kind of tool, the one that looks like the little angle with dots, the Right Angle Tool. This one will draw a right angle from whatever you are using. Use it to draw a rectangle around that little dock. 
  • Continue tracing the line up the coast. Feel free to use the line tool extensively and not get too bogged down in the minuteness of the curves. This can be edited later, and in the case of this tutorial doesn't need to be 100% exact. Continue to the very end of the railroad point on the Hudson River side and then stop.  
  • If you want to go on and trace the course of Spuyten Duyvil and the Harlem River, you can, but I'll be working with just this coastline for the rest of the module. 

Editing and Merging Lines in a Feature Class

Maybe you're happy with how well the lines that you drew came out and you're happy to move on to the next step and merge them. If you aren't happy with them, don't worry, you can do a little bit of tweaking to get them just so without having to redraw them entirely. 

  • Zoom in more so you can better see the line that you drew and how close it is to mirroring the line on the 1879 map. I've adjusted with the little dropdown at the bottom of the map to set the map to a 1:650 scale. 
  • I'll also change the Symbology  in the Coastlines feature class to be red and be 3px wide so I can better see it. 
  • Up at the top of the screen in the Edit set of tools is going to be the Edit Vertices tool
  • When you choose the Edit Vertices tool your line segment will transform into a series of green boxes and blue dots. You can use the green boxes to change the locations of these points on the line, and the blue circles to change the angles at which those green boxes are connected to each other. 
  • Similar to the other tools you commit to the edit by double-clicking. When you want to change which segment you are editing, just double-click on the green or blue dot you are working on and then click on the next one to select it. 
  • When we've gotten to the end of the original line that we drew, let's zoom out and see if we like the contour that this one traces more than the last one.  For what I've done, the answer is yes. So let's take all those line segments and make them one by merging them. 
  • Right-click on Coastline in 1879 in the Contents pane and choose Attribute Table. Using the Switch Selection tool at the top, select all the rows in this sheet, they represent all the line segments in this feature class. 
  • Go up to the Edit toolbar at the top and select Merge from the icons in the little scrolling menu where Edit Vertices was. You might have to scroll. 
  • This opens the Merge menu which will list all the segments that you plan to Merge together. While we're in there, let's also edit the <Null> next to Body Of Water to instead say Hudson River. Once you have this set up, click on the Merge button. 
  • Once it goes through, there will be only one row in the Attribute Table  for Coastline in 1879. Unselect it using the Clear tool. 
  • To better see what it is this new line feature class tells us, uncheck the visibility on OldMarbleHill.jpg to see what its coastline looks like against the modern Hudson River coastline in Inwood. It looks like there's a lot of extra coastline created artificially since 1879. 

Creating a Polygon Feature Class

So we've created a line feature class, what if what we want to outline on a map isn't a border but is instead a building or region? We can create a feature class that features polygons the same as a county map or other map that's using 2D shapes. In this case, we'll be tracing the outline of Inwood Hill Park on the modern basemap so that we can then look at that same shape on the 1879 map to see what properties, houses or other landmarks from that map are now just part of the park. 

  • Unclick the visibility for both the OldMarbleHill.jpg layer and the Coastline in 1879 layer since we're just going to be creating a feature class based on the basemap this time. 
  • Right-click on OldMarbleHill geodatabase in the Catalog pane and choose New  and Feature Class. This will open the Create Feature Class window. In this first window, let's name it ModernParkFeatures with an alias of Modern Park Features. Uncheck the Z values box, leave the box about adding the output to the map checked, and then choose Next. 
  • The next window is the one where you can add fields to your feature class. In this case, let's just add one with a Name of ParkName and leave its Data Type as Text. We are only planning on outlining Inwood Hill Park, but in case we wanted to add in other parks later to see what was on the map there in 1879, we'll be able to add those polygons and differentiate them from Inwood Hill Park. 
  • For the rest of the windows, we'd only be selecting the default options anyway, so let's just click Finish and it will get to work creating our new polygon feature class. 
  • It'll add this layer to your Contents pane. Let's change the symbology to something with a 2pt green border and no fill inside by right-clicking on Modern Park Features and choosing Symbology and then editing the symbol with the Format Polygon Symbol menu.

Creating a Feature in a Polygon Feature Class

  • The same as with the line feature class, you access the tools you use to create and edit features in the Edit toolbar. Choose Create and when it opens the Create Features window on the side, choose the dropdown next to Modern Park Features see the available feature tools. 
  • The main one that we'll be using is that first one, irregular polygon, considering how irregular the park shape is, but there's also a tools to draw a rectangle, an oval or a circle, depending on what features we want to be creating. 
  • Similar to what we did with the lines, we'll want to be creating polygons rather loosely for merging later, don't try to outline the entire park at one go, that's a ticket for frustration. 
  • Let's try the rectangle tool first. It's important to note that it only works to create a shape that consists of right angles and has only four sides. So if you have a building or something that is a strictly regimented square this will be a good tool. 
  • That doesn't seem to work all that well with the shape of this park. So I'll use Ctrl - Z to get rid of it. 
  • There's a better option, the polygon tool, it's the option you see that looks like a squiggly object that's the first in the row. This will let you create a shape of any amount of sides and with any kind of angles within it. You just draw that first line, and then click whenever you want to start a new line off of your existing one, and proceed from there. Double-click when the shape is complete. It takes some practice though, so be aware of that. 
  • Use the polygon tool to encompass any areas with straight-lined borders. Don't worry about overlapping with polygons you've already created.  
  • If you have any locations you need to outline that contain curves or other irregular borders, you can use the freehand tool, the one that looks like a little squiggle. This one functions differently than the freehand line tool, you're just drawing the borders of the shape that you wish to create, so it's a little trickier. The closer you get to connecting the end of your line to the start, the less guesswork it will do in completing your shape. And if you don't create the perfect border on your shape, don't worry, you can use the same kind of edit tools available to you in the line feature class to refine it. 
  • Let's continue outlining the park with whichever tools we feel most comfortable using. Remember:
    1. We'll merge all these shapes later so if it is easier to create smaller shapes that better fit the borders we want to draw, that's better than a bigger shape with borders that don't trace the outlines of the park all that well
    2. If the borders aren't totally perfect, we can use the edit tools to adjust them later. Personally, unless there's a curve involved, I prefer the polygon tool. I'm first going to outline all the angular bits of the park that are inland before I start getting to the coastal sections. 
  • Once I've finished, it looks something like the below. Not too exacting, huh? That's okay, because I'm going to merge all these shapes in the next step and do some refinements with the editing tools. 

Merging in a Polygon Feature Class

Before we start editing anywhere we were a little clumsy with the borders of our polygon, let's merge all the polygons that we created into one so we can better see if there are any gaps.

  • Right-click on Modern Park Features and choose Attribute Table.
  • There's lots of rows, and each of them is one of the polygons in our shape above. Make sure you have none of the rows selected, and then choose Switch at the top of the Attribute Table to select all the rows
  • Go up to the Edit toolbar and choose the icon for Merge. This will open a window with a list of all the different features you want to merge, and give you the option to merge their attributes as well. Next to ParkName type Inwood Hill Park. When you have that set up, click on the Merge button at the bottom. 
  • The Polygon will shift to now show a shape that's mostly one solid shape. I say mostly, because in my case it looks like I'll still have some work to do, as it looks like I didn't overlap the poygons that I created quite as neatly as I thought. 
  • Whoops! Fortunately, I can just draw another polygon that contains the mistake areas where clearly things didn't overlap as I planned, and then do another Merge
  • To deal with that large rectangle I somehow managed to not select just to the left of the Henry Hudson Parkway, first I'll use the Edit tab to get back into the Create Features mode I was using earlier, then I'll create a polygon that encloses it entirely
  • Once I've created this polygon, I'll select it alongside the existing polygon that consists of the rest of the park and then use Merge again to merge the two and there will no longer be a weird hole in the middle of the polygon that represents the park. 
  • Repeat this step for any other missed lines or squares within the shape of your polygon. For issues with the edges, we'll be handling that in the next section using the edit tools. 
  • Now that I've cleaned up the various sections of my polygon where I had segments or small areas omitted from it, I'll get to work on any sections of its borders that don't match up with the park's border on the modern map. 

Editing Polygons in a Feature Class

  • If you were as unsteady with the freehand tool as I was or if you got too reliant on the polygon tool in cases where what you were tracing wasn't quite a straight line, you may need to touch up the borders of your polygon. There are a couple of tools that can help: Edit Vertices and Reshape
  • I'm going to start out where I can see that I made several errors both big and small, that little promontory island of the park where I sometimes overshot the actual feature I was trying to outline and included some of the river, and sometimes undershot and didn't go all the way to the edge of the water. I'm going to also decide now exactly at what scale I need this map's borders to work, as what I'm generally doing this for is to compare this to the georeferenced map, so I don't need it down to the square foot, but perhaps say, 1:900? Higher?
  • First, I'll start with that large section where I apparently decided to include a whole lot of the water. Since this is a straight line that I just need to move down, I'll use the Edit Vertices feature. When I click on that, it turns the borders of the polygon into a series of green boxes which are the vertices, and blue circles which can change the angles that the vertices are connected at. 
  • In this case I'll just tug down the green box where I've extended my border too far until it matches up with the actual borders of this little peninsula, or at least as near as I can get it. 
  • I can drag over more of the green squares from the right hand side too to help complete the extra vertices I need to add. 
  • Similar to other edits when you've finished, you can just double-click and it will finalize your edit.
  • If you want to edit in a more freehanded fashion, you can use the Reshape option. For instance, for the sections where I undershot the border I wanted to draw, I'll choose the Reshape option, then click and use the cursor to encircle the sections I want added to the borders. Keep in mind if you want to extend the shape you'll need to start your shape within the polygon,
  • To use the reshape to make the borders smaller, you start drawing your shape outside of the polygon, click whenever you want to create a point for the line to pivot around and then double-click when you are done. 
  • Use whichever combo of these tools works best for your purposes. Maybe you're more comfortable with Edit Vertices, maybe with Reshape
  • Remember to periodically save your Edits with the little disk icon in the Edit menu marked Save
  • When you've finished, save the edits one more time. 

Polygon Feature Classes and Map Layers

  • Now that you've finished your polygon feature class go ahead and increase its size to 4pts in the symbology menu.
  • Turn back on the map layer for the 1879 map, OldMarbleHill.jpg and with the overlay of Inwood Hill Park, you can now see which streets and houses and properties have been swallowed up by the park.
  • If you want to better see if any of these old structures or roads still have traces in the park, make sure you have OldMarbleHill.jpg selected in the Contents pane, and then select Appearance under Raster Layer in the menu, and turn the transparency up to about 50%. This will make that layer partially transparent.  It looks like one of the trails in the park still follow Bolton Road, Prescott Avenue and Emerson Street to some extent

You could add other parks or sections to this map if you wanted, now that you have this feature class created.

Saving Your File

  • Click on the Project icon at the top of your menu bar and choose Save. If you are on your own laptop and don't plan on sending yourself a copy of your file to open elsewhere, you're all set. However, if you want to open this project file in another computer, or if you want to send your professor your project because it's finished or because you have a question, this is only part of what you need to do to ensure that you'll be able to access the project later. The other steps will need to occur in Windows Explorer, so exit ArcGIS Pro. 
  • Navigate to the path that your project was saved to at the beginning of this lesson, and locate the folder OldMarbleHill
  • Go back up a level to where your OldMarbleHill folder is locatedRight-click on it and choose Send to and select Compressed (zipped) folder
  • Windows will create a zip file of your project folder with your project file in it along with all the other files that it depends on. This zip file is what you will want to save to your Google Drive or flashdrive in order to access this project later if you are not just using ArcGIS Pro on your personal computer. 
  • If you had any issues creating this file, and need to see how I had it set up, here is the zip file that I made. The file I created in this lesson is called OldMarbleHill_NewFeatures.