Ohio/Boundaries/Counties

County borders were originally supplied by the USGS. Those boundaries are not of great precision. Also, that import process created a lot of overlapping ways, and didn't use the admin_level=* key.

Much work has been done on the county boundaries. There is now a boundary relation for each county, and all county boundary ways have been split and merged as necessary so that only one chain of non-overlapping ways defines the boundary between any two adjacent counties. (Along Ohio's border, Ohio's county boundaries were merged with the TIGER-imported state boundary. Generally, the boundaries of counties in adjacent states have not been modified, and remain sourced from imprecise USGS data.)

There are still tasks to be done, however. Where county and city boundaries overlap, they should be merged; the merged boundaries should have admin_level=6, unless of course they're also part of the state boundary, which would be 4. The accuracy of the USGS-sourced boundaries can be improved, by following the endpoints of TIGER data or clues visible in the aerial imagery; these clues might include visible property lines, and especially natural waterways. Check USGS topo maps when in doubt.

Because the TIGER import was conducted county by county, roads ended up disconnected wherever they crossed county lines. Worse, where roads followed the county line (especially in northwestern Ohio), two duplicate roads were imported, each with names and route numbers specific to one side of the road. We've mostly finished fixing the road network along county lines, though some issues are still waiting to be found.

One of OSM's strengths is that all types of data coexist in the same database, allowing you to (for instance) find roads that run along county lines without having to conflate two separate databases. Ideally, wherever a county or municipal limit clearly follows a road, river, or edge of a landuse area, we should "weld" the boundary relation to the other feature. For example, where the Butler–Hamilton County line follows Fields-Ertel Road, there is a way way that belongs to the Butler County Butler County and Hamilton County Hamilton County boundary relations. It is joined to Fields-Ertel Road Fields-Ertel Road at every node along the road. (In Potlatch, press F repeatedly to "follow" the road you're welding the boundary to.) Please do not make the road itself a member of the boundary relations.

*Boundary Sources:

• U: USGS data import
• M: USGS topographic map
• T: TIGER data import (state/municipality borders)
• Y: Yahoo! or other acceptable aerial imagery
• t: Implied from non-boundary TIGER data