OpenStreetMap
I uploaded a large batch of GPS data from my survey of Wompatuck State Park (Massachusetts, US) during the summer of 2008. This data contains multiple high-density traces from all paved roads and all trails in the park, except closed areas.
I'm planning to use this data for some well-needed cleanup of the park. OSM (probably based on TIGER data) is wildly inaccurate in this area at this point (just like, it seems, all other online mapping services).
Discussion
Comment from andrewpmk on 19 February 2009 at 07:12
This is actually MassGIS data, which is considerably more accurate than TIGER data, but still inaccurate in some places.
Comment from Ahlzen on 20 February 2009 at 21:29
Ah, of course... you're right. From working with both TIGER and MassGIS road data in the past, it appears to me that either the latter is based on TIGER or they just share many of the same issues. Nevertheless, you're probably right the MassGIS is generally higher quality.
Either way, Wompy could certainly use some work... :)