[Imports-us] Geopolitical divisions in Ohio

[Minh Nguyen]

Hi David,

Apologies for the late response; I don't read the imports list often. As 
an active mapper in Southwest Ohio, I thank you for your interest in 
improving this part of the map.

On 09:50 2014-02-25, David Days wrote:
> Greetings, all.
>
> I am a new user to OpenStreetMap, but a long-time software developer.
>   Currently, I'm working on a project that would benefit from having
> political subdivisions in the state of Ohio represented on a map.  A
> quick run through of the import history page doesn't show any similar
> data sets, so it appears that the results could be a worthwhile
> contribution.

The TIGER import left a ton of correct-only-if-you-zoom-out boundaries 
for counties, cities, and villages, but inexplicably omitted township 
boundaries. I've been manually entering township lines and correcting 
existing TIGER county and city/village lines off and on for the past 
year or so, but it's a neverending task and an import would be much more 
efficient. To my knowledge, there haven't been any imports specific to Ohio.

> To clarify, "political subdivisions" means not only the standard mapping
> features (city, village, county), but also township, voting wards and
> precincts, congressional districts, etc.  Some of these divisions are
> atomic (don't cross other jurisdictional lines), while others can cross
> several larger groups.

OSM needs Ohio township boundaries. They're stable and much more real 
than the CDP boundaries that came with the TIGER import. However, I 
would draw the line at structures that lack any governing body. (CDP 
boundaries never should've been imported.) Voting districts are better 
suited for external databases that can be "mashed up" with OSM, 
especially since, at least in theory, a county board of elections can 
completely redraw its precincts for each election.

> The intent is to start with one county at first, then expand as the
> project grows.  That translates into roughly 100 subdivisions, of which
> 75+ are non-city/town/village in the first data set.
>
> I'm planning on getting local experts within the areas described to
> manually create the mapping features at first, but eventually I would
> like to take other public domain data that's coming available and import
> it on a large scale.
>
> (As for licensing and reuse--the political divisions themselves are
> public domain, and I'm the owner of the project; even though the primary
> purpose is narrow, I thought that OSM and everyone else could benefit
> from having this map available).

Where does this data come from? Would it be feasible to start out by 
publishing a tile server that mappers could manually trace atop? That 
way, we can accurately align boundaries to real-world features (roads, 
creeks, edges of farms, etc.) when it makes sense to.

> With all of that in mind:
>
>  1. Good idea, ok, or really, really bad idea?
>  2. Reuse of existing datapoints is probably important (these divisions
>     usually follow clear boundaries, so finding existing boundary or
>     markers would cut down on the import size).  Pointers or gotchas?

Out-of-state mappers are often confused by the relationship between 
cities/villages, townships, and counties in Ohio. Cities and villages 
can span multiple townships and multiple counties. Some cities and 
villages have "withdrawn" from their townships, leaving a hole at 
admin_level=7. Some cities are no longer fully withdrawn: recently 
annexed land may still be part of a township. It's hard to get these 
details right without careful research or some contacts on the ground.

You'll find that the county lines (from the USGS), city/village lines 
(from the Census Bureau), and CDP lines (from someone with a vivid 
imagination at the Census Bureau) often disagree. If your data set turns 
out to be more accurate, perhaps we should try to align existing 
boundaries to your data in a manual import.

>  3. Import scale:  Ohio has 88 counties, with probably 100 of these
>     subdivisions on average.  If the entire idea is acceptable, would
>     per-county imports work better for the community, or would it be
>     better to get it all together and push it all at once?

I would suggest starting by reaching out to active mappers in the metro 
areas, to see if anyone would be interested in helping out with a manual 
or closely-supervised import in their immediate area.

Unfortunately, not every part of the state has an active community to 
speak of. You might be able to enlist some mappers from the big metro 
areas to help out with Southeast Ohio, for instance, but there isn't a 
whole lot for an armchair mapper to go off in those hilly areas.

>  4. Maintenance:  Most of these areas are pretty stable--about 100 out
>     of the whole state get reworked every 10 years.  Is this a factor,
>     and how much commitment to maintenance should I factor in?

If I recall correctly, annexation laws got stricter several years back, 
so city and village boundaries are mostly stable, even among the suburbs.

-- 
minh at nguyen.cincinnati.oh.us