map projection -- different shp files

hi all,
i got shp files from two sources. one from the demo of umn. the other
one from esri (sample maps). they both contains information of USA.
however, they do not align. i think the projections are different. how
can i know what projection a shp file is using? one shp file does not
come with a prj file.
and once i find that out, how can i convert from one projection to
another?

many thanks,
MJ

MJ,

If you are using ESRI Arc Products, you can check your projection by
right clicking on the shp file in the table of contents, you will get
the properties screen, under the Source tab if you scroll down it will
give you the shp files projection.


meijoen@yahoo.com wrote:

On 15 Sep 2006 08:45:46 -0700, meijoen@yahoo.com wrote:


If one of your shape files lacks a .prj file - and it is not part of
the specification, though is is usually provided - then you may be
unable to proceed. It is impossible to guess projection parameters,
especially where the projections may only differ in the datum used,
for example. It there are common features, then it would be possible
to transform the unknown data to the known, but you are in a better
position than I to decide whether this is appropriate or desirable.

I would approach the providers of your data and ask them for the
projection details, which you could use to construct a .prj file.

Best wishes

Paul