Here the process I have been using:
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Download OSM highway=path/footway/bridleway/cycleway/track
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Buffer by 15 meters (~49 feet). This is somewhat arbitrary, but the US National Map Accuracy Standard for 1:24K maps is 40 feet if I recall. So this gives the government data the benefit of the doubt.
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Subtract buffered OSM from government data
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Flag any trail in the government data where more than 40 meters (somewhat arbitrary) or 50% of the original length remain after the subtraction.
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Manually review all of the above flagged trails using imagery, Strava Heatmap, USGS 3D Elevation Data, other government sources (e.g. USFS has written descriptions for many trails, which doesn’t necessarily agree with its own GIS data, also, any new trail is required to go through an approval process that includes a spatial component, and those documents are available online), my own GPS traces, GPS traces others have uploaded to OSM, geotagged photos I have taken (for name, number, and allowed uses). I also sometimes make phone calls to local officials, visitor bureaus, etc to ask about the existence of certain trails and whether they are official, what their names are, and what uses are allowed.
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Any government trail that remains after the review is considered an error, although in some cases there is conflicting evidence, or no evidence, and these trails go into a third category which will require an in person survey.
In other news related to this general topic, I have been added to the invite for the TWG Zoom calls.