Geography

Learning Goals

Maps from a given era can be very useful to you as a historian, they can help you understand how parcels of land have changed over time, and tell you something about your subjects' lives. If you are studying a geographical area and have found a map that is of the correct time-frame and boundaries to be useful to you, you can take an additional step to add value to it by georeferencing it. Georeferencing is the process of taking what is called a raster (as opposed to vector) image and putting 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 to it 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 data. 

With this tutorial you'll take a historical map downloaded from the New York Public Library that shows the original location of Manhattan College and georeference it to a map of the same area today. I'll be attaching the image below, but if you want to find more information about it, it's available at: http://digitalcollections.nypl.org/items/96737d39-3456-fb23-e040-e00a18067dcb

Data

Getting Started

• Download SanbornMap_1909.jpg and save it to either a folder that you have already connected to ArcGIS via the Catalog window, or one you can easily navigate to do so. 
• View the image first in Image Viewer to take note of the area of Manhattan covered in the map. 
• Right-click on Folder Connections in the Catalog window and choose Refresh. Make sure that you can now see SanbornMap_1909.jpg amongst your folder's contents. 
• Go up to the Add Data icon in your menu bar. It has the same icon as the Layers but with a + sign on top. Click to open the dropdown and choose Add Basemap.
• Pick a basemap that will easily allow you to see the names of streets, since knowing the names of streets will allow you to more easily add anchor points. I'm going to go with OpenStreetMap but if you prefer Streets or one of the others granular enough to have street names, feel free to choose those. 
• Use the Zoom tool to zoom in on approximately the same area that you'll eventually be georeferencing your map to. 131st and Broadway. Remember, you can always click on the magnifying glass tool and draw a box around the area that you are interested in.
• Go to the Catalog window. Click on SanbornMap_1909.jpg. It should have an icon that looks like a grid next to it. Drag it onto your canvas. You'll get a warning saying that the data source is missing spatial reference information so it cannot be projected. You already know that it is lacking this information, and what you are going to do when you georeference it is add that spatial information so click OK.
• Your Table of Contents window will switch to List By Source and display SanbornMap_1909.jpg as a layer, but the display on your canvas won't change.
• Right-click on SanbornMap_1909.jpg and choose Zoom to Layer and you'll see that it does actually exist on the map, it just doesn't appear over the section of the city that you would like it to. To locate it correctly, you'll need to georeference it. 
• Go back to your OpenStreetMap  layer and zoom back in on the region of map that interests you, between 131st and 133rd streets bordered by Broadway and Amsterdam. So that you can find your way bak to this section at any point, create a bookmark by going to the menu item Bookmarks and choosing Create Bookmark. It will ask for a name, I'll choose Previous MC Location. 
• Now, if at any point I leave this location, I can always get back to it by going to the menu item Bookmarks and choosing Previous MC Location.

Adding Georeferencing.

You add georeferencing to a raster item by adding anchor points to the item and to the map beneath it where the two share a common location. When you add enough of these, ArcGIS will be able to rectify the two items, and accurately stretch and place the raster item over the locations on the basemap that it covers. 

• Open the Georeferencing toolbar by going to Customize on the menu bar, choosing Toolbars and then Georeferencing. The below toolbar will appear hovering on your map. The photograph you are trying to georeference will have its name within the dropdown and you will mainly be using the icon with the two Xs connected with an arrow, Add Control Points.
  
• You'll next be choosing anchor points that you'll be placing at the same location on both maps. So switch back and forth between the two and write down at least 4 intersections or features that you know exist on both. Notice that some intersections that exist on the 1909 map don't exist any more on today's map, such as that between 130th Street and Old Broadway.  You should add far corners and points of interest first
• Make sure that you are within the SanbornMap1909.jpg layer and click on the Add Control Points icon, then click on the corner of West 133rd and Amsterdam on the side where you do see details of buildings, the northwest corner.  You'll see a crosshairs appear in green on that corner, and the number 1 will appear. A long line will come out from that number when you move your cursor around from it
• Go to Bookmarks and choose Previous MC Location. When you move your cursor, you'll see that it's still an X with a band coming off it.
• In your Table of Contents, click on OpenStreetMap to make sure you're adding that layer. Use the scroll wheel on your mouse to zoom in over the same northwest corner of 133rd and Amsterdam and click. 
• Click to uncheck the box the SanbornMap_1909.jpg layer, to make it no longer visible. Then find the same corner on your OpenStreetMap layer and click on it. This creates the other half of that anchor point, and will move the SanbornMap_1909.jpg until it is sized to fit over those points. 
• Repeat next for the corner that the old location for Manhattan College was, 131st and Broadway. First on the SanbornMap_1909.jpg layer and then on the same corner in the OpenStreetMap layer. You'll have to un-check the box on SanbornMap_1909.jpg as it is stretched over that map. 
• When you click to make SanbornMap_1909.jpg  visible again  you'll see that the map is already pretty close to centered over the right parts of the map. 
  
• You can look in on how the anchorpoints are moving the map by clicking on the last icon over with the two arrows within a window, View Link Table. 
• It lists the links, and you can see what the margins of error are in that last column over, Residual. Ideally, you want to have smaller numbers in this column, but when you have problems with the scale of your map, like that roads are drawn larger in the map than they are in the current iteration of the city the way they are now, then you just might want to delete any outliers with huge residual numbers. At any point you can just highlight a link and click on the item with the X at the top, to eliminate it. 
• If you want to test and see if your map changes if you eliminate a link, you can just uncheck the box next to it. 
• You can also use the dropdown marked Transformation to test how different transformations with anchorpoints will change how your map appears. It can be anything from only a slight distortion, to items such as Spline which will distort anywhere on your layer being georeferenced without an anchorpoint to ensure that the areas with anchorpoints are a complete match, it will look something like the below. I'll be going with the default option.
  
• When you like how your map is lined up, click on the dropdown, and choose Update Georeferencing which will save these coordinates to your photo. You can also choose Rectify which will make a new dataset out of your photo. 

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 SanbornMap_1909.jpg and choose Properties. It will do some processing since this is the first time you have looked at the properties for this layer. 
• In the first tab General, you'll notice that the Description and Credits fields are blank. 
• Where it says Credits write

  ---

  New York Public Library

  ---

  since that is where you got the information

• For the description, go to the address in the introduction for where this book was located on the New York Public Library's website: https://digitalcollections.nypl.org/items/96737d39-3456-fb23-e040-e00a18067dcb and on that page choose Cite This Item.

• That will bring you to the area on the bottom of the page that contains how to cite this item in several different styles. For an actual paper you will want to double-check this citation against a style guide, but for this map, you just want to be sure you have adequate information for a viewer to understand what they are looking at, so paste in the paragraph under APA contents in the box for Description. 

Lionel Pincus and Princess Firyal Map Division, The New York Public Library. (1884-). Manhattan, V. 11, Plate No. 3 [Map bounded by Broadway, W. 133rd St., Amsterdam Ave., W. 130th St.] Retrieved from http://digitalcollections.nypl.org/items/96737d39-3456-fb23-e040-e00a18067dcb

• ​Click OK to save the description and credits that you've added. 

When you are done, save your map. You can see how mine came out if you look at the below.

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 features what was on the blocks surrounding Manhattan College in its former location. You'll create and edit a feature class of this area, by referring a georeferenced map created from old maps of the area layered over the current maps, and add labels for your new shapes. Then you'll save all relevant files into a geodatabase so other users can look at the items you created if they want to expand your project.

Data

Getting Started

• Open GeoreferencedAreaAround_FormerLocation_MC_Layered.mxd  in ArcMap and take a look at it. There are multiple maps layered on top of each other that were  all scans from an old fire insurance map at the New York Public Library. 
• It isn't optimum for clarity in its current state but since you are only looking to take a few buildings' locations from it, this is fine and you won't need to clip it. 
• Since you'll need this information later, find out the Coordinate System being used in your data frame by going to Layers, right-clicking and choosing Properties.
• In the Data Frame Properties window, go to the Coordinate System tab and write down the Projected Coordinate System and Geographic Coordinate Systems that you see there: WGS_1984_Web_Mercator_Auxiliary_Sphere for the first and GCS_WGS_1984 for the second.
• You'll be placing the feature class that you're creating in a file geodatabase. This is a structure that you can place different feature classes and raster data sets in so that you have one compact place to store all your data. 
• In the Catalog window, go to the Home folder where you have been storing your data, right-click and choose New > File Geodatabase.
• Name your new geodatabase 1909GeoreferencedLayers.gdb
• Right-click on that geodatabase and choose New -> Feature Class

​Creating a Feature Class

• In the New Feature Class Window give it the name BuildingsOfNote1909, and the alias Buildings Of Note Near Manhattan College, 1909. The name field will not allow spaces so use them in the alias
• Make sure that the Type dropdown is set to Polygon Features. A feature class can only store point, line or polygon data. In this case you'll be adding individual features that are polygons that represent the buildings on the map that you are interested in. Click Next.
• Make sure that the current coordinate system matches the one you wrote down earlier, GCS_WGS_1984. Click Next.
• Use the number already populated for the XY Tolerance in the next field and click Next. Leave the default selection for the next window about the database storage configuration.
• This next window is important because it will contain the fields available to you to enter information in about the features that you are drawing. Basically the fields that will be on your attribute table. There are two created by default. OBJECTID which has the unique ID for the object, and SHAPE which contains that the item in question is a polygon.
•  By clicking on the empty rows below OBJECTID and SHAPE, you can add your own new fields. Start with NAME, and for the Data Type, select Text. The field properties will appear below in a window.
  • Ignore Alias in this case but that is where you would put a clearer name if rules for character length and spaces make it difficult to give your field a comprehensible name.
  • Leave YES as the answer for Allow NULL values since you want to be able to leave the field blank if you need to research further information
  • Default Value is where you would put in what you want the field to be if you don't put in another answer. This can be helpful if you have a field that you know will always or almost always have a given value on a feature class you are created.
  • Length is the amount of characters that will be allowed in this field. I'm going to change this to 250
• ​Create another new Field Name, PURPOSE. It's type will also be  Text, and leave the default values in for its properties, except for Length which you should also make 250.
• Click Finish. Your new feature class will be added as a layer at the top of your map in your Table of Contents and assigned a default symbol, but your map won't have changed because you haven't put anything in this feature class yet. If you click to expand 1909GeoreferencedLayers.gdb you'll also see that there is a new feature class in it called Buildings of Note 1909

​

Now that you've created a feature class to use to trace the outlines of Manhattan College and other buildings around it, you'll need to add features to it.

Adding Features to a Feature Class

• Turn off all the layers but SanbornMap1909_West130-133_MC_Broadway_Amsterdam, since you'll be using a lot of processing power, so it makes sense to look at these one by one.
• Right-click on Buildings of Note Near Manhattan College, 1909 and choose Edit Features > Start Editing. You'll get a warning, but ignore it.
• If you don't already have the Editing toolbar active, go up to Customize -> Toolbars -> Editor. At the far right of that tool, there is an icon that looks like a pencil next to a checklist of items.
• This will open a new window with Create Features  at the top. Select the layer Buildings Of Note Near Manhattan College, 1909  and at the bottom where it says Start A Template click and select that you want to use an Auto Complete Polygon construction tool
• Zoom in over Manhattan College and click at one of the corners, you'll see it creates a block with a line coming off it. Stretch that line around to the side of the building and click whenever you want to set an end point and change the direction of the line. When you are done, you'll get something that looks kind of like this

​

• Click on the icon that looks like lines within a piece of paper, this is will open the Attributes Window.  Below that is the layer name, and the unique ID for the feature you just created. You'll see that the fields that you created NAME and PURPOSE have <Null> as both their values. Change the name to Manhattan College and the purpose to Higher Education.

• Now if you click on your Identify tool up top, and then click on the outline you drew, you will get a pop up that lists the same values. And if you click to turn off the layer containing the georeferenced Map you'll get a view of this building on top of the building that has replaced it as it appears on the basemap.

• You can also use other tools to draw features, for example the Rectangle tool which will let you draw a first line and then stretch it out at right angles beyond it. Use this to draw a feature around the Smith & Kaufmann Silk Ribbon Manufactory at 132 near Old Broadway that you can see if you scroll up and left from Manhattan College.
• Add the Attributes to this shape of NAME : Smith & Kaufmann Manufactory of Silk Ribbons, PURPOSE: Factory
• The Polygon tool can be useful for items that are not perfect rectangles but do contain square rather than round shapes. Scroll over on your map until you see the J. Hood Wright Memorial Hospital (It's at the corner of West 131st and Amsterdam)
• Click on the Polygon item under Construction Tools, and then click on one of the corners of the hospital. You'll notice that now when you move to the next line, it drags the line with it as well as the color that will eventually be the color of your symbol. 

​

• When you have drawn a line around the borders of the whole outline of the hotel, double-click on the last point and it will create your new feature. Go to Attributes and fill out the name and purpose of the building. 
• If you don't like how the feature has been constructed you can go up to the triangle shaped tool on the Editor toolbar, this lets you edit the vertices. There are also tools to let you split the polygon if you realize that you went to far outside the shape. 
   
• You can draw circles too if you need, go to the Table of Contents and turn back on the layer SanbornMap_1909_West130-133_Broadway_12th and locate the circular tank between 131st and 132nd street. 
• Go back to the Create Features window and select the Circle tool from the Construction Tools  menu. This turns your cursor into a drawing tool 
• Go to the center of the Standard Gas-Light Co.  Gas Holder, and click. Then draw out the circle to cover the edges of the tank as it appears on the map. Double-click to finish your circle shape. Add its attributes on the Attribute window.
• If you don't like it's placement, select it, then go to the Editor dropdown and select Move then 
• The Ellipse tool can also be good for circular shapes. Scroll up to the second circular gas holder between 132nd and 133rd at Riverside.
• In the Construction Tools menu, select Ellipse, this turns your cursor into a drawing tool. Draw a line out from the middle point of the circle, click and then move out the circle that emerges until it is covering the entire feature
   
• Using these tools, turn on the other layers one at a time and create a feature for at least three buildings per layer. Make sure that you always fill in the attributes for Purpose and Name. Pick buildings of at least 5 different purposes.
• When you are finished, go up to the Editor toolbar and choose Stop Editing.

When you've added a bunch of shapes to your map for buildings you'd be interested in superimposing on today's map, move onto the next step and change the symbology of the tabs to reflect their purpose.

Changing Symbology on a Feature Class

You can proceed from the map that you created but if you want to follow along with the categories for purposes that I created, it is below.

Data 

Getting Started

• If you are using my copy, open it in ArcMap. 
• For either file, right-click on Buildings Of Note Near Manhattan College, 1909 and choose Open Attribute Table
• Scroll through the Attribute Table to see what field makes sense to visualize with Symbols. The Name column seems to have a lot of variation, whereas Purpose has a variety, but several of the categories are repeated so it makes sense to use this as a key.

Adding Symbology and Labels to a Feature Class

• Right-click on Buildings of Note Near Manhattan College, 1909 and choose Properties.
• Click to the Symbology tab and in the Show menu choose Categories. Click PURPOSE in the Value Field dropdown and then click on Add All Values
• This will add all the available values in PURPOSE and assign them colors. You can click on any of them to edit the color assigned. I recommend reserving green for items like parks and farms so as not to be counter intuitive, but you can come up with the classifications that you'd like. When you aren't duplicating any colors and they seem intuitive, click OK.
• Your map should now look something like this. See how many places you can work out are the same and how many different. You can be aided in this by clicking on the Display tab in the Properties window and changing the percentage next to Transparent to something like 20%.
  
• Add Labels to these features by right-clicking on the layer and choosing Label Features
• The first try will look like quite a mess though, but you can edit the labels to make them clearer, just double-click on Buildings Of Note Near Manhattan College, 1909 to open its properties window and navigate to the Labels tab.
• Click on Symbols and then Edit Symbol. In the General Tab change the Y Offset to 1, and make the text bold.
• In the Mask tab choose the Style button next to Halo  and make the Size 1.5.
• Click OK  twice and then your map will have nicer looking labels
• You can customize them further by using the Labels  toolbar, get it by going to Customize > Toolbars > Labeling
• From that toolbar use the labeling dropdown and choose UseMaplex Labeling Engine which will let the text be wrapped.
• When you are fully zoomed out the labels still look kind of cluttered. You'll want to change the Scale Range so that you only show the labels when you are zoomed in enough that they they are informative instead of a confusing jumble. 
• Zoom in until you like the way the labels look. This happens for me at 1 in = 0.03 mi. 
• Double-click on Buildings Of Note Near Manhattan College, 1909 to open the Properties window and navigate to Labels. Click on Scale Range.
• Click on the button next to Don't show labels when zoomed and in the dropdown for Out beyond: choose <Use Current Scale>.  Leave the dropdown for In beyond alone and click OK. and then OK  for the Layer Properties window. 
• When you return to the map if you use the Pan tool, or zoom in, you'll still see the labels but if you zoom out, they'll disappear.

You've now created a labeled map with edited features. If you want to see how I constructed mine, it will be in the attachment below.