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Posted by Jean H on May 14, 2008, 5:25 pm
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Gary W wrote:
> I'm trying to create a map of our County with municipal boundaries
> superimposed, and several hundred points plotted. I'm using several
> open-source and/or free GISs, gvSIG, QGIS, and MapWindow GIS. I get
> identically wrong results in all three.
>
> The projection for the map layers for county and municipal boundaries
> are NAD83 UTM 18 (I believe this to be correct and pertinent... I'm
> very much a beginner). The point locations are in a shapefile with
> decimal latitude and longitude.
>
> All the 'map' layers overlay one another perfectly, but the points
> shapefile plots far, far away from the map it should be on top of
> (compared to the map of New York, the points appear south of where
> Florida would be, roughly in the caribbean.
>
> I am absolutely stuck on this... Can anyone point me in the right
> direction?
>
> Thanks very much in advance, --Gary
Hi again Garry,
ok, UTM18 nad83 is good for NY.
Most GIS systems can deal with layers having a different projection...
so you might have a problem in your shapefile. It sounds as if you have
declared as UTM the coordinates that are in LatLong. There are way to
change the projection (NOT to re-project) of a shapefile, though I have
no idea how to do it without ArcGIS. You might have to get back to when
you have created the shapefile, and to specify the proper projection
there (something like Geographic Coordinate System - WGS1984, or
projection code 4326 in gvSIG ).
Otherwise, if you are sure your layer is already defined as lat-long,
you might have to re-project the layer (in this case, the coordinates
are transformed from 1 reference system to another one). For gvSIG, look
in the manual, section 9.13 p339
At last, you could try to set the "view" in gvSIG to lat-long, then add
your points, then add the other layers.. they may be all correctly
located now.
Jean
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