Help with shape files - extent and projection

[Norbert Thieme]

Pablo Toapanta schrieb:

>Hi again
>
>I´ve tried everything to obtain a map file that works
>with my shape files but I´ve not obtained what I need.
>
>I think that is the projection and the correct size of
>the image.  Could anybody tell me if there is a way to
>know the correct projection and image size for a shape
>file??
>
>Thanks
>
>
>
>
>__________________________________
>Do you Yahoo!?
>New and Improved Yahoo! Mail - 100MB free storage!
>http://promotions.yahoo.com/new_mail
>
>
>
>
Pablo,

you can use ogrinfo on the shapefile to get the extent. With that extent
in your mapfile it should be possible to show the first image. Simply
leave all projection definitions out. You can do that for data which has
the same projection. So if you use one shapefile you don't have any
problem. The projection gets important when you want to use different
projected datasets or have a changing projection for the map (e.g. WMS).

For projections it is important that you know your data and you should
know the projection for providing a map service:
- ask your dataprovider
- sometimes you have additional information like a .prj file for
shapefiles or some other metadata like text or html files
- mostly data is in a popular coordinate system so you can often look at
the coordinates (if you are familiar with different projections) and
guess / try

The imagesize is only important for the outputed image so you can set
that to whatever size fits your site or application.

Regards,
Norbert