Geocoding a Mailing List to a QGIS Heatmap — Nominatim, MMQGIS, and Kernel Density Estimation
You have a CSV of postal addresses — a membership list, a customer database, a survey response set. Someone wants to know where these people are concentrated. A heatmap is the right output: it shows density without exposing individual addresses, it scales from 100 to 100,000 records without changing the workflow, and it overlays cleanly on basemaps, zoning layers, or any other spatial data you have. The full pipeline in QGIS: geocode addresses to coordinates using MMQGIS and Nominatim (OpenStreetMap’s free geocoding service), reproject the resulting point layer to a metric CRS, and run kernel density estimation in the QGIS Processing Toolbox. Three steps. The traps are in the rate limits, the CRS handling, and the distinction between two different “heatmap” tools inside QGIS that look alike and behave differently. ...