3-Layer Maps is a neighborhood search tool allowing you to find places that match one or up to three criteria of data on a map. For example, you could use it to find neighborhoods with high rates of children in poverty, but too little spending on Child Nutritional programs, or neighborhoods with high numbers of hospital visits, but low rates of insurance coverage. It's particularly helpful for finding areas with federal designations to invest in, like New Markets Tax Credit-eligible tracts in Medically Underserved Areas.
The tool can also be used to download a list of points in a dataset that fall within areas matching your criteria (using Download Points) or a list of places that meet the criteria (using Download Places). 3-Layer Maps is available to subscribers.
To start, select 3-Layer Maps from the upper left of the Maps page.
The page will look similar to the Maps page, with the Data and Location search bars across the top and data menus above the map. However, to the left you will see three legends; one for each data layer that you can add to the map. 3-Layer Maps allows you to use up to three data layers on the map at the same time. Adjusting the criteria ranges for each data layer as it is added lets you find only those places which meet all of the parameters.
To begin, enter a location in the Location search bar. You'll need to choose a location first, because 3-Layer Maps requires the map to be zoomed in.
Next, add a data layer from the data menu or data search bar above the map. A legend will display to the left of the map. In the legend for each data layer, users can change the year, the variable, and geography types by clicking on Edit Layer, and move the sliders or enter criteria values to set the ranges.
- When you load the first data layer, the map will be completely purple. This is because the map is showing the entire range for the data layer loaded. You can set a specific range by moving the triangles in the slide bar or entering values in the fields. The map will then shade only those places that meet the parameters in purple.
- Just like the legend on the maps page, users can change the year, variable, and geography type. Click on Edit Layer.
- Some data layers on PolicyMap do not have numerical ranges to set, but check-boxes for individual values. Unchecking a box will remove areas with that value from the shaded part of the map.
- To add additional criteria, choose another data layer from the data menus or data search bar.
- The areas shaded purple must match the criteria set for all layers. If an area matches only one layer's criteria, it will not be shaded.
- In some cases, the map will instruct you to zoom in further. The triangular symbol of the zoom bar will indicate how far you must zoom in to be able to see data. The farthest out you can zoom is determined by the smallest geography type in the data layers. A 3-Layer Map with census tracts must be zoomed in further than a map with counties. To make the map display, you can zoom in, or change the Shaded by geography type by clicking on Edit Layer.
If you are creating a 3-Layer Map at a national or regional level, then change the Shaded by to a larger geography so the data will display on the map without zooming in as far. You will need to do this to every data layer added.
Note: The map will always show the SMALLEST geography type identified in the legend. For example, if you have three criteria selected for census tracts, counties, and zip codes, the map will display census tracts that match all three criteria as that is the smallest geography.
- Click on any area to see values for all the layers you've added.
- You can also add point datasets, to see locations that are situated in and outside of the shaded areas.
After you have set up the criteria for a 3-Layer Map, you can save, share, and download the data.
There are two ways to download data from a 3-Layer Map.
- Download Layers allows users to generate a list of all geographies which met the criteria of the 3-Layer Map and the values for those places. Learn more about Download Layers.
- Download Points allows users to generate a list of points which fall in the shaded area on the map. Learn more about Download Points/Sites.
To read a full guide on all features on PolicyMap, please look at our Primer available here.