How this map was made

What the network rests on

47,773 km of trail, of which 8,078 km (17%) is drawn by two or more independent maps and 341 km by three or more. The rest is one map's word. Much of it — 22,086 km — comes from a single work, William E. Myer's 1928 synthesis of the Southeast's trails, which itself compiled earlier maps and journals.

50 more maps on the site are open for members to trace; each new map that draws a trail already in the network narrows its corridor. The route corridors (“compiled from published accounts”) are Native Routes' own summaries of 25 documented routes, drawn coarsely and weighted lightly.

How it is built

1. Placing each old map. Every source map is georeferenced: places on the scan are matched to where they are today and the scan is warped to fit. Each map gets a stated accuracy — the typical distance between something on it and its true position — from how well those places agree. Old maps are distorted; a map placed to ±30 km can still show a trail correctly relative to its rivers and towns. (Georeferencing method.)
2. Reading the trails. Trails printed in red are traced automatically from the red ink, cleaned of lettering and boundaries, and checked by a person. Other maps are traced by hand: points are read along a drawn path off magnified, gridded views of the scan and joined, either following the ink or, where roads, rivers and hill-shading crowd the line, straight from point to point (the reading error is far smaller than the map's accuracy). Members can trace trails too; a second member confirms each one.
3. Melding. Each traced line is a witness with an uncertainty of half its map's accuracy. Lines that run alongside each other for at least 5 km, in the same direction (measured over a couple of kilometres) and within 2.5 times their combined uncertainty, are taken as the same trail. The line drawn is their average, weighted toward the more accurate maps; its corridor — the shaded band — is the larger of that average's uncertainty and how far apart the maps actually are. Wherever the set of maps changes, the line is cut into a new stretch.
4. Counting maps honestly. A stretch's confidence counts independent maps: a member's trace counts as the map it was traced from; a route corridor drawn from a map counts as that map; several sheets or plates of one work count once; and a map only counts for a stretch if it draws at least half of it. Confirmed (solid, dark): three or more maps, each itself placed within ±20 km, agreeing within 5 km. Corroborated: two or more, each placed within ±40 km, agreeing within 10 km — a coarsely placed map can still add its line, but it cannot vouch for agreement finer than its own accuracy. Dashed: one map so far, however good.
5. Joining the network. Ends that come within a stretch's uncertainty of another trail are joined to it.
6. Bridging gaps over the terrain. Where one map's own line is broken — usually where lettering or a fold crossed it — and its two ends face each other, Native Routes bridges the gap with the easiest walking route over today's elevation data (Tobler's hiking function on the Terrain Tiles: USGS 3DEP and SRTM). A bridge is drawn only if both ends come from the same map, the gap is at most 30 km, the route is at most 25% longer than the gap, it climbs no more than 60 m per km, and it never joins two differently named trails; each was then checked by eye. 36 gaps (650 km) are bridged this way. They are drawn dotted grey, labelled as inferred, and never count as a source or toward any trail's length or confidence.
7. Nations’ lands at the time of settlement. The territories layer is the Indian Claims Commission’s 1978 map of “Indian Land Areas Judicially Established” (compiled by the U.S. Geological Survey; digitized by the National Park Service; public domain): the 176 areas nations proved, in cases from 1946 to 1978, they held when the United States took them. Each is joined to the Royce cessions over it for when it was taken, and to the present-day nations whose names carry its people’s names (nations whose ceded lands merely overlap it are listed apart). Outlines are simplified to about 0.5 km.
8. Lands ceded by treaty. The 266 nation pages and the cessions layer use the U.S. Forest Service's digitization, with the National NAGPRA Program, EPA and Claudio Saunt, of Charles C. Royce's Indian Land Cessions in the United States (1899) — 718 areas with the date of each treaty, law or executive order, the parties as Royce named them, and the present-day nations the dataset associates with each (data.gov, CC BY 4.0). Outlines are simplified to about 1 km.
9. Versions. Every change makes a new version with a changelog; a published version is never altered, so it can be cited. Each version's network, towns and source lines can be downloaded from the map.

Where errors are most likely

• Placement. The largest error: each old map can be off by its stated accuracy (from ±3 km to ±60 km here), unevenly across the sheet. The corridor shows this; the line inside it is a best estimate.
• Maps that copy maps. Many sources compiled earlier ones (Myer drew on colonial maps; later engravings copied surveys). Maps that look independent may share an ancestor, so “confirmed” can overstate agreement.
• Tracing. Automatic tracing can take lettering, boundaries or rivers for trails, and miss faint stretches; hand tracing can follow the wrong of two nearby roads on a crowded sheet. Straight point-to-point tracing cuts corners between the points read.
• What was recorded. The maps show the trails colonists and surveyors used or were told of, in their spellings, at the moment they looked. Many trails were never mapped; dates of retrospective maps (made long after) are approximate.
• Bridged gaps. The terrain bridges follow today's land surface, which includes reservoirs, cuts and fills, and the easiest route is not always the one people took. They may run in the wrong valley.
• Towns. Historic towns are shown only at about 1 km and only where a source names them as Native towns; sensitive places (burials, mounds, sacred sites) are deliberately left off.
• Nations’ lands. The territory boundaries are what litigation established, drawn for court: shared and contested lands are simplified into single claims, nations that brought no claim (or lost) are missing, and the East is thin because it was taken before such cases. Treat them as a floor, not a homeland’s extent. Matching them to present-day nations by name is ours and can miss or mislink.
• Cessions. A cession is when the United States took title, not where a homeland began or ended; overlapping claims, unratified treaties and land taken without any treaty are not shown as such, and the link to present-day nations is the dataset's.
• The base map. “Land as it was” hides modern roads and towns but still shows today's rivers and lakes, including reservoirs.

Credits

Base map © OpenStreetMap contributors (Protomaps). Elevation: Terrain Tiles on AWS Open Data (USGS 3DEP, SRTM). Treaty cessions: USDA Forest Service and partners, CC BY 4.0, from Royce (1899). Nations’ lands at settlement: U.S. Indian Claims Commission and USGS (1978), digitized by the National Park Service. Source maps: their makers and the archives that hold them, credited on each map's page. Traces by Native Routes and its members.