How to create a missing sidewalk map in QGIS

How to create a missing sidewalk map in QGIS
Missing sidewalks are highlighted in black here. 

If you've got a GIS map of your city's roads and a map of your city's sidewalk, you can use the QGIS software to create a map of your missing sidewalks. A missing sidewalk map can be useful to plan where new sidewalks should go or to audit transportation equity.

The steps I used are explained in this video and also below.

  1. Download and install QGIS if you haven't already. https://qgis.org/en/site/
  2. Obtain your City's road and existing sidewalk layers in a vector format if you haven't already. I used GeoJSON.
  3. Determine the latitude of your City. (Right click on Google maps, "What's Here?")
  4. Find the conversion between degrees to feet at your latitude. http://www.csgnetwork.com/degreelenll...
  5. In QGIS, use "Layer: Add Layer: New Vector Layer" to load each map layer.
  6. In QQIS, use "Vector: Geoprocessing Tools: Buffer" and select the sidewalk layer. Buffer it out 50 feet converted to degrees. For Bloomington, Indiana, the calculation was: (1/364160.86)*50
  7. In QGIS, use "Vector: Geoprocessing Tools: Difference", select the road layer as the Input layer and the buffered sidewalk layer as the overlay.

The resulting layer is a map of roads of with no sidewalks. The resulting map is not particularly clean. There's a probably a better way to create a missing sidewalk map. Let me know in the comments!

I wanted to highlight the missing sidewalk layer on another map, so I followed the process above to "buffer" it out 10 more feet. If your map display software supports handling this as a display/styling issue-- that's a better way to do it.

This was originaly done for the Sidewalk Equity Audit I conducted for Bloomington, Indiana.