[Talk-us] County lines vs. TIGER roads

[vidthekid at gmail.com]

On Jun 24, 2010 1:31am, Val Kartchner <val42k at gmail.com> wrote:
> Ah, so it USGS county lines that were imported. Can we get TIGER county
> lines imported instead, if they're more accurate? They should at least
> match the county assignments on the roads. We should leave the import
> to someone more experienced than me though.

> And what would we do about the county lines that have already been
> edited?

I would expect TIGER county lines to be much better than USGS, so an import  
of some kind would be nice. But I think there should be manual  
reconciliation / merging with existing data before anything is actually  
uploaded to OSM. In Ohio, a lot of work has already been done with county  
lines, including redrawing many of them from Yahoo! imagery, TIGER road &  
city boundary data, and USGS topos. Also, wherever a road follows a county  
line, any county boundary imported from TIGER will sit directly on top of  
that road already in OSM. For these reasons I recommend a mostly-human kind  
of import process. Maybe something like, the bot has a front end where  
mappers can request the import of a single county boundary segment at a  
time (by selecting two adjacent counties) which the bot will then create as  
a way, with minimal tagging. Then it would be up to that mapper to use his  
preferred OSM editor to reconcile / merge that new data with existing map  
features like roads, city boundaries, and the USGS lines.

On the other hand, in many places importing county lines from TIGER may not  
even be necessary. If the boundary is a straight(-ish) line, one can  
basically draw a line connecting the "ends" of the TIGER-imported roads, or  
if there's a road along the boundary, then use whatever method is preferred  
for mapping that. Also, county lines often coincide with property lines,  
which are often visible in aerial imagery. Where county lines follow  
natural features, these features are often visible in aerial imagery so  
drawing a new line isn't too problematic. With these techniques, I've  
achieved results that are probably about as good as the TIGER data anyway,  
and certainly better than the USGS lines.
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