Hi,
I'm very new to GIS and thoroughly enjoying it. I've already spent far too many late nights trawling GIS sites on the net just for fun

Anyway, I am currently working with the GLOBE 30 arc-second DEM database which gives me elevation data in nice neat 1x1 degree blocks and what I need to do is draw some of those blocks on my sensible linear X/Y computer screen and then overlay it with some items I have the Lat/Lon co-ords for.

Now - if just plot the GLOBE data, the images seem 'compressed' and I assume this is because I am not compensating for the longitude distortion as latitude increases/decreases. I've trawled and trawled the net looking for answers - so many projections! After three days, I _think_ I need Miller projection(?)

My big question is - what formulae do I need to transform both the DEM data and my chosen lat/lon locations so that they'll match up?

Phew - big question from a little beginner!

I would really appreciate any insights into this fascinating (for me) problem.

Very many thanks.

Hi FlyingSolo

What GIS software are you using? Usually, when loading geospatial data into GIS software, it either comes with projection information with the data (in many cases in a separate little file with the same filename as the data and with the suffix .prj) or the software asks you what projection the data is in. Assinging the right projection should result in the data being displayed seemingly undistorted. Distorted data points to a wrongly assigned projection.

Is the DEM data in Miller, or is Miller the projection your map should eventually have and the DEM is something else?

Some software allows for data to be be in different projections and still be displayed on the same map (ArcView calls this "on the fly projecting"). Most software also has reprojection tools built in, so you don't need to find the formula by yourself.

Hope this helps you get started,
Kathi