chiGRID divides Chicago into regular one-mile cells called chis, bounded by the
mile roads and centered on the half-mile-road intersection. Each chi has a public name like
Damen–43rd chi, a compact label Dam43, and a formal chi-ordinate
χ:5S3W indexing its position from State & Madison. Click a cell to inspect it.
Origin. The grid is anchored at State & Madison, the zero point of Chicago's address system. χ:1S1W is the chi at the origin; numbers grow south/north and west/east from there.
Limits & midpoints. Every chi is bounded by mile roads and centered on the half-mile roads between them. The Damen–43rd chi spans Ashland→Western (east–west) and 39th→47th (north–south), centered on Damen and 43rd.
Geographic, not address-number. Distances are real miles. Chicago's south-side street numbers overstate distance (43rd St is ~4.5 mi south, not 5.4), so the grid uses true geography — which is why 43rd lands in the 5S band and Ashland on the 2W/3W boundary.
Names. The x/avenue comes before the y/street: Damen–43rd, Dam43.
chiGRID sits beneath neighborhood and community-area names — it doesn't replace them.