Bivariate Mapping

Douglas/Sarpy Census and Background Map


This week, we are working with ArcMap to create choropleth maps for an Illustrator layout. ArcMap is the main component of Esri's ArcGIS suite of geospatial processing programs, and is used primarily to view, edit, create, and analyze geospatial data. It is a massive and complicated program. Our task is to simply make the required maps and save them to Illustrator format.

ArcGIS includes a number of background maps that can be used for spatial reference. These are pre-rendered raster files. This assignment shows how to add such a background.

Part I: ArcMap Steps

  1. Download this zip file: Douglas/Sarpy County
  2. The data are from the 2010 Census, and a combination American Community Survey data.
  3. Map block groups. While the Census Bureau collects data by household, it only provides data at specific levels of spatial aggregation. The smallest spatial unit used by the Census Bureau is the block. Blocks are usually not mapped because so much of the data is blocked for reasons of privacy. A series of blocks make a block group. A series of block groups makes a census tract. A series of census tract make up a county, and a series of county make a state.
  4. Choose two distributions to map.
  5. Does it need to be normalized? Most of the data needs to be divided by the total population of each tract/block group. This is called normalization.
  6. Choose an appropriate basemap (click arrow next to Add Data 'plus sign'). The background should help users identify actual locations. Backgrounds are pre-rendered raster files (tiles). It will become a separate layer. It's important not to add a transparency in ArcMap - otherwise, the entire map becomes rasterized.

Part II: Bivariate Renderer

  1. Go to Layer Properties>Symbology
  2. Choose -> Multiple Attributes
  3. Choose -> Bivariate renderer
  4. Select the two attributes you would like to map
  5. It is a bit buggy -- Probably a good idea to stick to 4X4 grid
  6. Pick Two colors that will combine well
  7. Click apply. Now to export the legend:
  8. Go to Layout view
  9. Insert Legend
  10. Make sure your Layer is in the box on the right side
  11. Resize legend and export

Part III: Illustrator Steps

  1. Choose the map sub-layer and add an appropriate transparency.
  2. Add title, neatline.
  3. Export as png and pdf. Add links to your index page.