Qagggy 
2008 v. 2023: I don’t think people realize the extent to which parked cars degrade public space.
Toon Van de Putte 🍉@qag Can confirm that a lot of people have become blind to parked cars, they don't even notice them anymore, they're so ingrained. Our mayor wouldn't believe that 90% of public road space was reserved for cars, until we pointed out that curbside parking takes up a huge amount of space, especially in narrow city streets. He'd simply not ever thought about that.
legumancer Davy@legumancer @qag Well, I'd be interested!
@legumancer @qag I don't have a specific project
@toon @qag this is the software I used https://www.qgis.org/en/site/
Data sources for the US:
https://www.usgs.gov/the-national-map-data-delivery/gis-data-download
https://www.census.gov/geographies/mapping-files.html
https://www.arcgis.com/home/group.html?id=24838c2d95e14dd18c25e9bad55a7f82#overview (I'm not 100% sure this would work on the open source program)
Some (most?) US counties have downloadable GIS maps with things like property lines, roads, utility lines, etc. County data may be what you want for local projects.
I did a project for class on the proprietary ArcGIS mapping bike routes between specific locations with wayfinding + weighting the preferred-ness of roads based on speed limits, # of lanes and whether there is a bike lane.
I used the free version to identify land parcels of a certain size that were near either a water or a sewer connection and on a road - basically trying to identify land that would be good for building on without excessive cost.
Another college project was using aereal photography to map the % of cattails vs invasive phragmites grass in a wetland. You could probably do something like that to map parking - manually draw shapes and let the software calculate area.
If looking for land for a community garden, you could use the county building code to find out what makes a lot *un*buildable, then have the software highlight unbuildable vacant lots for you. From there, the owner's mailing address might be available online, or you might have to ask a county office to look it up. Now you have a list of owners of low $ value land who might be convinced to sell it to a garden co-op. You could even narrow it down further by eliminating parcels next to buildings older than 1970 or so and busy roadways (soil contamination from high lead content paint and vehicle emissions), parcels with too steep a slope, etc.
@toon @qag I'm not sure if car accident data is publicly available, but if it is I bet you could do some interesting qgus analysis with that.
Census data includes info like race, income and age of the people who live in each census block, so it can be useful for checking what's unfair in your city. A lack of grocery stores in low income neighborhoods is one of the classic ones. I bet you could look at speed limits on residential streets in each census block too, and look for bias in the traffic laws.