History UnderfootAtlanta

Methods and sources

Methods and sources

Every place on the map carries its own sources and says when a location is approximate or the sources disagree. This page explains the layers underneath and how the lake work was done.

Water

Lakes start from the U.S. Army Corps of Engineers' National Inventory of Dams, matched to lake outlines from USGS hydrography, plus lost lakes, mill ponds and ponds the inventory misses. Average depth in the inventory is normal storage divided by surface area, so treat it as rough, and the inventory's "year completed" is often a rebuild or survey date.

Streams are the USGS high-resolution stream network. Buried and piped streams are modeled: the USGS lidar was resampled to 10 m, its pits filled, and every cell routed downhill to trace the paths water takes. Paths draining more than 0.2 km² that no mapped stream follows are shown as buried or piped where the ground around them is at least 20% paved or built (NLCD 2021). Road fills and culverts bend the model, so a line marks the valley, not the exact pipe. Watersheds and divides are from the USGS Watershed Boundary Dataset.

Reading the aerial photos

Each of 87 lakes got its own stack of aerial photos, from the 1940 mosaic to the most recent county or federal flight, cut to the same frame, plus a shaded view of the bare-earth lidar. An AI agent read every stack year by year: when the lake first appears, when it was low or drained, when it disappeared, and what the lidar shows of the dam, any breach and the old bed. A second agent checked each reading against the images and flagged anything it could not confirm. A lake's status changes on the map only when the photos show it full and later gone.

The photos are from Georgia State University Library's map server (1940 to 2013), DeKalb County's imagery services (2001 to 2026) and USDA NAIP (2023). Photos are not dated to the day, so "drained in 1982" means between two photos unless a record says more.

Watermarks

22 lost and drained lakes are put back on today's map in two ways.

Each Watermark names the photo it was checked against and lists its caveats, such as a lake that runs off the edge of the frame. On the map the refilled lakes get the same treatment as Glen Emerald Lake: shaded by depth, with contour lines, the deepest spot marked, and a water-level slider that fills them from the bottom up. Three cases, with the old water level 2 ft lower or higher, bracket the uncertainty, and tapping the water reads the depth at that spot.

Depth

67 lakes have a depth model. Where the lidar was flown while a lake was low, depth is measured: the old pool level minus the ground (9 lakes). Elsewhere it is modeled from the shape of the shoreline, deeper toward the middle and toward the dam, and scaled so the average matches the dam inventory's average depth, never deeper than the dam allows. Modeled lakes get three cases, at 0.7, 1 and 1.35 times the inventory's average depth. Modeled depths are estimates; no bottom survey was found for these lakes.

Imagery and lidar

The 1940 to 2013 aerials and the 1921, 1938 and 1950s maps come from Georgia State University Library's map server (the Sprawling of Atlanta mosaics, the 1949 Aerial Survey of Atlanta and the Planning Atlanta collections). Everything was reprojected to one grid, so layers line up to within a few meters; the oldest mosaics are less exact at their edges, the 1940 mosaic has missing frames in DeKalb, and the 1949 survey and the maps cover only the city of their day.

The county-wide ground model is USGS 3DEP lidar. The lake work uses DeKalb County's 2024 lidar wherever it reaches. The shaded view lights the bare earth from the northwest; the micro-relief view subtracts a smoothed surface so only small bumps and dips remain, which is where old grades, dams and ditches show.

Civil War, Segregation and Early

The 1864 lines come from the Georgia Historical Commission markers Wilbur Kurtz wrote in 1956, the Official Records (vol. 38), the National Park Service battlefield survey and, for the Confederate inner line, Emory's ATLMaps fortifications layer. They are drawn on today's streets where the sources name the roads and inferred between documented points; each popup gives its confidence.

The segregation maps are the City of Atlanta's and the Atlanta Regional Commission's own, from GSU Library's Planning Atlanta collection. The 1938 grades are from Mapping Inequality. The 2000, 2010 and 2020 figures come from the Census Bureau's redistricting files for each census's own tracts. Words like "Negro" appear because they are the maps' own titles.

Land lots and districts are from DeKalb and Fulton County GIS, which still use the 1821 survey. Trails are drawn along the modern roads that sources say follow them and should be read as corridors, not paths.

Research and checking

Entries were compiled in September 2026 from the New Georgia Encyclopedia, the Atlanta History Center, the DeKalb History Center, National Register nominations, Georgia Historical Society and Historical Marker Database markers, the Official Records, National Park Service battle summaries, newspapers and magazines, court opinions and published scholarship. The lake histories alone cite 407 distinct sources across 631 timeline entries.

AI research agents drafted the entries, and a second AI pass checked 4,167 claims against their sources and corrected 1,211 of them. Timeline entries are labeled documented, likely or uncertain. The About page has more on how AI was used.

What is left out on purpose

There is no layer of probable Native American sites. Georgia keeps archaeological site locations confidential because published locations get looted and many sites include graves, and a predictive map would amount to the same thing. The public map also leaves out the Civil War artifact-likelihood model and anything that reads as advice on where to dig. Parks, cemeteries, preserves and state land are no-dig by law.

Credits and licenses

Text written for this site is licensed CC BY 4.0. The images and datasets above keep their own terms; please follow them if you reuse anything.