Mosaic
Mosaic
Mosaic is a program for computer-aided redistricting using recombination and simulated annealing. Load a shapefile, choose the goals that matter for your project, and let the algorithm repeatedly redraw and score the map. Start from scratch, load an existing assignment, or continue refining the map on screen.
Follow the current plan during a run. Color the map by election results, demographics, compactness, or population deviation, and show county lines, precinct lines, district labels, or split counties.
Choose how many changes Mosaic should try and how closely district populations must match. Annealing controls how freely the search explores as the run progresses.
Mosaic normally redraws two neighboring districts at a time. Optional three-district moves and single-precinct flips give the search additional ways to change a plan.
Turn individual scores on and set their weights. Available goals cover population balance, district shape, county splits, elections, demographic geography, and alignment with a reference plan.
Open history charts for individual scores, track where goals align or compete, inspect district details, and return to the best plan found during the run.
Save the current assignments and district metrics as CSV, or save the map as a PNG or PDF.
Install on Windows 10 or 11, or an Apple Silicon Mac. You do not need to install Python yourself; the launcher handles setup on the first run.
Installation guide →