Dallas city limits, 1855–2022
The city as it annexed its way outward, from the 1855 town of a third of a square mile to the 385 square miles of today — built from the annexation ordinances themselves, so the boundary moves in the years it actually moved. Every piece of ground carries the ordinance that took it in.
About the sources — and how much of the city the ordinances explain
Two datasets from City of Dallas GIS, doing different jobs. The spine is
Annexations — 776 ordinances from 1900 to 2016, plus 89
de-annexations, each a polygon carrying the date it passed, the date it took
effect, and its ordinance number. Mirrored by
src/land/annexations.py. The head of the timeline comes from the
older historical city limits series, nine digitized snapshots
1855–2022 (src/land/city_limits.py), because nothing in the
ordinance record reaches back past 1900. So 1855 and 1875 are snapshots, the
1900 boundary is the base the ordinances build on, and everything after 1900
is assembled a year at a time from the ordinances themselves. Nothing is
fetched at page load; the city's disclaimer applies (Tex. Gov't Code
§ 2051.10).
How well the two agree. Testing the ordinances against the independently digitized snapshots — sampling points on a 400 m grid inside each snapshot boundary and asking whether an ordinance in effect by that year covers them — the ordinances account for 97.7% of the 1940 boundary, 97.7% of 1960 and 98.5% of 2000, once points within 600 m of the edge are excluded to strip the generalization mismatch between the two datasets. The remaining one to two per cent is interior ground inside the city that no ordinance polygon covers. Those gaps are real and they are visible on this map as holes; they are not patched, because patching them would mean drawing boundaries the record doesn't support.
One quirk worth naming: the city's annexation layer opens with a single 1900 polygon that has no ordinance behind it, and its note says it was traced from “Sam's Streets Map of Dallas County, 1900 City Limit Line” and “may need to be corrected”. That is the same sheet this project hand-traced for the 1900 chapter of the main map, so the city's ordinance mosaic and our own tracing rest on a shared source at their base. This page uses the snapshot series' 1900 boundary instead and leaves that record out of the counts. Sixty-four later annexations also carry no ordinance number, mostly between 1903 and 1915; their popups say so.
De-annexations are drawn on top in the page's own background, which subtracts them visually. That is a drawing trick, not a geometry operation — the underlying annexation polygon is still in the data, and its popup still works, which is arguably the honest representation of a piece of ground that was taken in and later let go.
For this project the ordinances that matter are 4389 (1948) and 5658 and 5659 (1952), which brought the old La Réunion colony land inside the city. 5658 records its ground as taken from Eagle Ford — the settlement next door to the colony, annexed out of existence. The twenty-year snapshot series could only say that the colony land was outside in 1940 and inside by 1960; the ordinance record names the instrument and the date.
The colony lands on the modern map → · The two towns of 1855 →