[Talk-us] CDPs and admin_level

David ``Smith'' vidthekid at gmail.com
Mon Oct 12 09:42:53 BST 2009

In most states, municipal boundaries have been imported from TIGER
data.  In many of these states, no admin_level tag was used.  That
should be corrected (admin_level=8 for incorporated municipalities)
but that's not the focus of this discussion.  In the states where
these boundaries were imported with admin_level=8, it appears that
Census-Designated Places [1] were also included in the import, and
treated the same as incorporated cities.  (That's what happened in
Ohio, anyway.)  The wiki page [2] that lists what admin_level to use
for various administrative units in different countries does not
address Census-Designated Places.  It does not say that CDPs should be
admin_level=8, or any other value.  I believe this should be

Census-Designated Places are geographical units determined by the
Census Bureau to give (arbitrary) limits to otherwise-unquantifiable,
informal population centers.  They do not represent any real
political, governmental, or administrative unit.  There are no signs
posted to mark the borders of a CDP.  Residents of a CDP usually are
not even aware of its existence, though they are certainly aware of
the informal population center it's meant to represent.  They really
have minimal real-world significance.

You may be asking yourself, 'but how can I tell if something is a CDP
or an actual city?'  There are a few ways.  For one thing, you could
look up the locality on Wikipedia.  CDP boundaries typically follow
only roadway centerlines and sometimes county boundaries, whereas
actual corporation limits can and usually do also follow property
lines and the edge of the right-of-way on one side of roads.  (More
correctly, CDP boundaries don't split census blocks.)  Finally, the
answer may lie in the tags generated by the boundary import.  For
example, in Ohio, there's a tag like tiger:LSAD which always ends with
" CDP" if the entity is a Census-Designated Place.

I suggest using admin_level=9 or admin_level=10 for CDPs.  If there is
agreement here, then the wiki should be so clarified.  (I don't think
a full-blown proposal is necessary to make a minor clarification to an
existing map feature, do you?)

[1] <http://en.wikipedia.org/wiki/Census-designated_place>
[2] <http://wiki.openstreetmap.org/wiki/Tag:boundary%3Dadministrative#admin_level>

David "Smith"
a.k.a. Vid the Kid
a.k.a. Bír'd'in

Does this font make me look fat?

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