[GRASS-user] Alaska shapefile crosses 180th parallel

Brent Wood b.wood at niwa.co.nz
Wed Feb 21 16:36:39 EST 2007

Paul Van Deusen wrote:
> I'm trying to read in the state boundary shapefile from 
> http://nationalatlas.gov.  However, the Aleutian Islands
> cross the 180th parrallel, so longitude goes from +180 to -180 at that 
> point.  I end up with the end of the
> Aleutian Islands getting disconnected.  What is the solution?  I used 
> v.in.ogr and set up a location using the information that came
> with the shapefile.  See spatial information below.

Welcome to my world! (oceanic GIS around New Zealand :-)

Reproject to a non lat/long coordinate system, or convert the longitudes 
to a 0-360 space instead.

If you use PostGIS, shp2pgsql the shapefile, then run a query to 
translate all features with a component with long<0 by 360 on the X 
axis, then add these back to your original dataset, then pgsql2shp this 
to a new shapefile.

It works for me :-)

FYI, I'm submitting a request to EPSG to have 2 lat/long projections, so 
as well as EPSG:4326 which defaults to +-180, we have an EPSG code for 
the same projection with a 0-360 long space. I don't know how they'll 
feel about it, but we'll see...


Brent Wood

> Spatial_Reference_Information:
>  Horizontal_Coordinate_System_Definition:
>    Geographic:
>      Latitude_Resolution: 0.000278
>      Longitude_Resolution: 0.000278
>      Geographic_Coordinate_Units: Decimal degrees
>    Geodetic_Model:
>      Horizontal_Datum_Name: North American Datum of 1983
>      Ellipsoid_Name: GRS1980
>      Semi-major_Axis: 6378137
>      Denominator_of_Flattening_Ratio: 298.257222
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