[Gdal-dev] Shapfiles and Projections

Tue Oct 9 14:55:07 EDT 2007

Hi everyone,

The second link sometimes appears dead, but here is cut-and-paste from the document.

.shp- the file that stores the feature geometry. Required. 
.shx- the file that stores the index of the feature geometry. Required. 
.dbf- the dBASE file that stores the attribute information of features. Required. 
.sbnand .sbx- the files that store the spatial index of the features. Optional. These two files can be created in ArcView. See ArcView's on-line help for more information. 
.fbnand .fbx- the files that store the spatial index of the features for shapefiles that are read-only. Optional. These two files can be created in ArcView. See ArcView's on-line help for more information. 
.ain and .aih - the files that store the attribute index of the active fields in a table or a theme's attribute table. Optional. These two files can be created in ArcView. See ArcView's on-line help for more information. 
.prj - the file that stores the coordinate system information. Optional. This file can be created with and is used by the ArcView Projection Utility. It is not used by ArcView GIS Version 3.x or older versions, or by ARC/INFO versions previous to version 8.0. 
.xml - metadata for ArcInfo 8.0, for using shapefiles on the Internet. Optional. 
A good summary of the file types used by ESRI.

Cheers,
Dean
----- Original Message -----
From: Dean Mikkelsen <dcmikkelsen at shaw.ca>
Date: Tuesday, October 9, 2007 11:43 am
Subject: Re: [Gdal-dev] Shapfiles and Projections
To: eschenbe at psc.edu
Cc: gdal-dev at lists.maptools.org

> Hi Kent,
>  
> The Shapefile technical definition can also be found here:
>  
> http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf
> 
> and 
>  
> http://facweb.knowlton.ohio-
> state.edu/selhami/crpinfo/teaching/CRP608/Shape%20file%20structure.doc 
> Note that the .prj is optional and was a late addition to the 
> Shapefile definition (not sure myself when it came along, but it 
> was not present in the Original White paper).
>  
> Cheers,
> Dean
> 
> ----- Original Message -----
> From: Kent Eschenberg <eschenbe at psc.edu>
> Date: Tuesday, October 9, 2007 11:08 am
> Subject: Re: [Gdal-dev] Shapfiles and Projections
> To: gdal-dev at lists.maptools.org
> 
> > Thank you all for your assistance. The gdal/ogr library can 
> read 
> > the shapefile 
> > if the directory also contains the dbf and shx files that came 
> > along with the 
> > shp file. Specific responses below.
> > 
> >   -----Original Message-----
> >  > gdrinfo doesn't seem to find a projection in a 
> shapefile 
> > describiing roads
> >  > (from the National Atlas). I was expecting something 
> > like what gdalinfo
> >  > finds in a geotiff file. Could someone point me 
> towards 
> > the answer?
> > 
> > Martin Chapman wrote:
> >  > Make sure there is a .prj file with the same name as 
> the 
> > .shp file.  NTAD
> >  > data doesn't always come with these projection 
> > files.  If you read the .txt
> >  > file with the shape file it will tell you what datum 
> it 
> > is using.  Attached
> >  > is a wgs84 prj file that should work if you rename it 
> to 
> > be the same as your
> >  > .shp file.  NTAD is generally in WGS84.
> > 
> > Hmmm ... I didn't do that; there is no prj file but it now 
> seems 
> > to work.
> > 
> > Ed McNierney wrote:
> >  > Unfortunately, the concept of projections and 
> coordinate 
> > systems in general
> >  > was late in coming to the shapefile format, and many 
> (if 
> > not most)
> >  > shapefiles have no projection/coordinate information 
> > with them.
> >  >
> >  > Your shapefile should have a .txt file with it 
> > (presumably roadtrl20.txt
> >  > if you're using the roads layer from the National 
> Atlas) 
> > and it will
> >  > contain this information:
> > <clip>
> > 
> > Yes, a txt file was supplied and it has information similar to 
> > your example. 
> > However it doesn't seem to be used. I'm still developing my 
> > application and so 
> > I'll find out soon enough if it is needed by hiding or not 
> > hiding the txt file.
> > 
> > Frank Warmerdam wrote:
> >  > I assume you were using ogrinfo?
> >  >
> >  > It will report coordinate system info if it finds 
> > it.  Does your shapefile
> >  > dataset include a .prj file?   If not, there 
> > is not declared coordinate
> >  > system for the file.
> > 
> > Yes, my mistake, I am using ogrinfo. No prj file was supplied 
> > but it seems that 
> > information was provided in the txt file.
> > 
> > Kent
> > Pittsburgh Supercomputing Center
> > _______________________________________________
> > Gdal-dev mailing list
> > Gdal-dev at lists.maptools.org
> > http://lists.maptools.org/mailman/listinfo/gdal-dev
> > 
> 
> Dean C. Mikkelsen, B.Sc., P.Eng.
> Terra ETL Ltd.
> Victoria, B.C., Canada
> Phone: +1 (250) 361-6672
> http://www.terraetl.com
> 
> Consulting in Geodesy & GIS  for the Natural Resources
> 

Dean C. Mikkelsen, B.Sc., P.Eng.
Terra ETL Ltd.
Victoria, B.C., Canada
Phone: +1 (250) 361-6672
http://www.terraetl.com

Consulting in Geodesy & GIS  for the Natural Resources
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