[Talk-us] Systematic problem with GNIS import and elevation tags

Alan Mintz Alan_Mintz+OSM at Earthlink.Net
Thu Mar 3 03:46:13 GMT 2011

At 2011-01-30 18:44, Paul Johnson wrote:
>I just noticed while researching node 357412228 that it has the
>following properties (mostly) imported from GNIS:
>Node id=357412228 lat=36.0747997 lon=-95.9005176 (projected:
>x=-95.9005176, y=36.0747997); Data set: 4B68BE0E; User: [id:92286
>name:Paul Johnson]; ChangeSet id: 6CCAA4; Timestamp:
>2011-01-30T02:34:15Z, Version: 4
>   tags:
>     "gnis:created"="08/01/1994"
>     "gnis:county_id"="143"
>     "name"="KCMA-FM (Broken Arrow)"
>     "FIXME"="This tower exists, but it's not KCMA."
>     "gnis:feature_id"="1102236"
>     "gnis:state_id"="40"
>     "man_made"="tower"
>     "ele"="261"
>I added the FIXME, but otherwise it is as it was imported from GNIS.  Of
>concern:  The ele= tag is described in
>http://wiki.openstreetmap.org/wiki/Key:ele as being metric value,
>however, this was obviously imported as Imperial, and incorrectly at
>that (FCC has elevation of 264.3 feet).  Clearly 261m isn't the correct
>elevation, but it is numerically closer to it's foot value.  I'm
>wondering if the person who imported GNIS originally has plans to change
>ele values that match their GNIS values by
>(current ele) * 0.3048 = (corrected ele), and if not, how we should
>handle this as a community.

There are a couple of things going on here.

1. The actual ground elevation near the base of the antenna appears to be 
about 870' (265m), so the ele tag is correct (no units implies meters).

2. Moving slightly to where I perceive the base of the tower to be, and 
converting to NAD27 datum (as used in the FCC searches), I get no AM or FM 
broadcast records anywhere nearby:

*** 0 FM Records within 1.00 km distance of 36° 4' 29.20" N, 95° 54' 0.80 " 
W ***
*** 0 AM Records within 1.00 km distance of 36° 4' 29.20" N, 95° 54' 0.80 " 
W ***

Taking a peek at the tower in G, it can't be an AM broadcast antenna 
because there are many antennas mounted to it (for AM broadcast, the tower 
itself is the antenna). I also don't see an FM broadcast antenna on it 
(though it could be a single dipole and it's too fuzzy too see).

3. I do get an ASRN 1047282 that is off a couple hundred feet, but appears 
to be the right record. It claims ground elevation of 264.3m, which is 
consistent with the other sources. BTW, since not all towers require an 
ASRN,  the next thing I would have tried is to search the ULS database for 
1000-29999 MHz and then 30-1000 MHz. Once you learn which services to 
ignore, you get decent site info.

Alan Mintz <Alan_Mintz+OSM at Earthlink.net>

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