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Topozone/USGS GNIS

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Topo Zone uses Nad 27. To see its variation plug in your house coordinates and see where it comes up in your neighborhood.

USGS can use both datums depending on the date of the map.

If you use TOPO software from Nat. Geographic you can put in what datum you want the map to be at, all the calculations are done for you.


Tahosa - Dweller of the Mountain Tops.

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As noted above, NAD27 is primarily used for Topozone. The GNIS database is inconsitant. Much of the database uses NAD-27 coordinates. But, like Topozone, the use is not universal.


GNIS positions are also often off a bit anyway because they are often taken from printed reference materials. The Space Needle would be a good example. If you look on an aerial photo the spot seems to clearly miss the building, but if you look at the USGS topographic map, the dot is placed squarely on the buildings next to the label.


I've converted all the GNIS FTP files to WGS-84 and placed them online in a searchable format. Drop me a note if you are interested. It's free, but saying the site name is apparently grounds for moderation of my messages... icon_wink.gif



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