ArcGIS doesn't just allow you to place points, polygons or lines representing geographic locations on a map, it will also allow you to analyze those points using tools from within its geoprocessing toolkit. This can help you narrow down which areas are most pertinent to your study and find out important information about those areas.
In this exercise we'll be determining which schools in Brooklyn are within 1/8th of a mile (walking distance) of a green space using different geo-analysis tools in order to clip our files to just the borough we want, to create a buffer around the schools of an eighth of a mile, and then detect where those buffers intersect with one of the green spaces.
The question you'll ultimately want to answer is what areas of Brooklyn contain both a public school and a sizable park within an eighth of a mile? To do that, you'll first need to narrow down your selections to just Brooklyn using the Clip tool, then create a buffer of .125 mi around the green space using the Buffer tool, then use the Intersect tool to find just the schools that are within that boundary.
The Clip tool allows you to take a layer with a larger geographic range than you need, and clip it to match the outline of a smaller layer, creating a new feature class with that smaller area. This can be handy if you are studying a smaller area like a group of adjacent counties or census tracts but can only get basemaps that encompass a whole state or region. You can clip those larger maps to just the area you need which eliminates confusion and frees up processing power. In this case, you were only able to get maps of where public schools and green spaces were located for the whole of New York City's five boroughs, but you only want to look at the ones in Brooklyn
The Clip tool allows you to trim one layer to match the geographic boundaries of another. We'll be using it on the PublicSchoolLocations and GreenSpaces layers rather than the Definition Query that we used on the BoroughBoundaries layer for a couple of reasons. Firstly, it's just easier to use this tool on the green space layer because there isn't an attribute field for what borough the green space is located in. Secondly, even though Definition Query controls the size and shape of the BoroughBoundaries layer as it appears, the extra information is still available and so taking up space when the map is being processed. We won't need information on public schools or green spaces that aren't in Brooklyn, so we may as well create a new layer that doesn't contain that information to save on processing speed.
Now that you have the layers that contain only the information that you need, you can process that information much easier
The Buffer tool is used to create a new layer that expands out the boundaries of a point, line or polygon a specified distance in all directions. That distance can be the same for all objects, or you can decide it based on one of the fields in your attribute table. For instance, maybe you are looking into environmental hazards and have different kinds of chemical plants mapped that each have a different minimum safe distance. Instead of creating a uniform buffer of a mile for each, you could create a buffer layer that had 1/4 mile for plants that had that listed as their safe distance, 1/2 a mile for plants with that safe distance and so on.
In this case you're just looking to create a buffer zone around polygons in the GreenSpaces_Clip and the points in the PublicSchoolLocations_Clip layer of 1/8 of a mile out so that you can see which areas have both features in close proximity.
On the map though, you'll see that some of the parks are large, and others seem to just be narrow sections of roadway. So you'll want to do another Definition Query to narrow down the parks that are being shown as just ones over a certain amount.
Your map should now look something like the below, with less parks because you are only showing the ones with larger areas on them
Now you can add a buffer to these parks and see which schools are within an eighth of a mile of these parks.
You'll now look for where the two layers overlap with the Intersect tool.
You can use the Intersect geoprocessing tool to look for where two different layers coalesce and making a new layer with that information
You'll notice that when you zoom in and out or pan the map, it can take some time to redraw these layers, because any individual circle can have multiple intersections due to there being multiple parks' or schools' buffers which intersect. With the Dissolve tool you can turn these many different intersections into one layer. This is a tool that is useful mostly if you don't care about any of the other attributes (if say, you don't want to know which elementary school and which park a given intersection is near). You can keep some amount of information about the individual interesections by choosing a layer to make the dissolve based on. For instance if I wanted one of these shapes to just consist of all the occasions where an elementary school overlapped and another to consist of all the times a high school overlapped I'd make the Dissolve Field SCH_TYPE. Or if I wanted there to be a separate shape based on each park, I could make the dissolve field park_name.
And now you've created a layer with only 22 shapes one for each district, rather than one for each intersection.
If you want to see how this works as a finished product it's attached below.
With ArcMap you can do more than just run the tools that individually come with your toolbox, you can create your own model. A model lets you string together a series of geoprocessing tools into a workflow. When you have finished creating your model you can run it using specified map layers and data, and can even set it up to perform the same tasks on different tables or layers. Additionally, a final view of the model works excellently as a illuminating graphic you can use in your paper or project to explain to the viewer exactly how you processed your data.
With this exercise, you'll be working with a similar map to the one you created last time that showed the areas of Brooklyn that were within 1/8th of a mile of both an elementary school and a green space. You'll create a model that will process the intersection of those areas with areas that are within half a mile of a public library to further analyze which parts of Brooklyn are short walks from institutions important for child development. When this model is run, you'll get a new map layer that displays the intersection of these areas.
In the last exercise, you went through multiple steps, some first on one layer, and then on another, in order to create a map that used open GIS data to illustrate where in the city was within a short walk of a public school and green space in Brooklyn. Since you now know which geoprocessing tools can be used to create this map, you'll next be adding those same tools to a model which you can then run and automate your process. This model is going to be stored in your toolbox.
A model consists of data (layers, feature classes, tables, shapefiles) and tools with connections made between them. You can use not only data that you already have on hand, but also the data that occurs when a new layer is created as a result of a task being performed on an existing layer.
You used tools from ArcToolbox in your last exercise, in this one you'll make your own toolbox that contains a model combining different processes that accomplish a task.
A model is a visual representation of a process you'd like ArcMap to do. Data is represented by blue ovals, rectangles represent tools, and green ovals represent the output of a tool. Tools and the ovals representing outputs are represented as clear if the tool still requires inputs or parameters to function. The items get a drop shadow after they have been performed when you run the tool.
If you ever have issues locating where a tool is you can do a search for it by pressing CTRL F to open the Search window.
You have now in a few boxes and arrows done the same thing as the first couple of steps for the previous exercise. It should look something like this.
You've created a layer BK_Facilities that has already clipped the shape file with all the facilities in New York City to just contain those in Brooklyn. Now you can use the Select tool to narrow that new layer down further to just those in the subgroup of Public Libraries.
The Buffer tool creates a new layer with a buffer circle at a given distance from every point in a layer. Like the other tools used on an individual basis in the last exercise, you can add this tool as part of a model and create a buffer around your layer with the public libraries in Brooklyn that shows the area a half mile in every direction of a library.
The Intersect tool will look for the places where two layers intersect, and export a layer containing only those intersections. This can be handy when you are looking for only areas meeting certain criteria within a larger geographic unit like a city, state or country. Like the other tools in the last exercise, it can be added to the model. You'll add this tool calculating the intersection between EighthMile_Diss and the new layer you just created with the buffer around the public libraries.
When your model looks like the below, you'll be set to save it. Save it as PublicLibraryBuffer
When you only have the intersection layer on the map, it should look something like this.
Suppose having run this model, you want to add one more process on your final layer - the Dissolve tool used in the last module. You could just run it using ArcToolbox, but if you wanted it to be part of the model (if you wanted to send someone your model if they wanted to base their research off it), you can add it to the model now, and run that step.
If you want to see how I have constructed my map, it is attached below, along with a jpeg of how the model was constructed.