Retail site selection consultants charge thousands of dollars for trade area reports. The underlying work is a drive-time polygon overlaid with census demographics, with competitor locations plotted on top. All of it is reproducible with PostGIS, free government data, and open commercial data from Overture Maps.
Most database problems are fixable. A slow query gets an index. A hot table gets partitioned. A node runs out of memory and you add another. The feedback loop is tight enough that you can experiment your way to a better configuration without touching application code or migrating data.
The last couple of posts in this series described navigation algorithms: robot vacuums covering a living room floor, then self-driving taxis doing the same at city scale. In that second post, I mentioned that Waymo vehicles sweep lidar continuously to sense the road around them. That’s lidar as a real-time perception tool. There’s another side to it: aerial terrain surveys that produce large static datasets, published and publicly available, and queryable with SQL.
A developer asked me recently which open data sources he could use for real-time traffic in his application. The list is shorter than he expected, and the main reason is licensing.