Overview
GTOPO is a Digital Elevation Model dataset (DEM) with a horizontal grid spacing of 30 arc seconds. You can view an example here http://edc.usgs.gov/products/elevation/gtopo30/gtopo30.html
You can read more about it here.
Add a Gtopo30 File
Adding a Gtopo30 to GeoServer is very easy.
1) Simply navigate to the Config->Data->CoverageStores->New menu:
2) Select the Gtopo30 Coverage Format dataset option.
3) Enter the name you want to use for the dataset in the Coverage Dataset ID field. Then hit New.
4) You will be taken to the CoverageStore edit screen where you will have to enter the path to your Gtopo30 file. You can enter a relative path to your data directory if that is where the file lives, or you can enter an absolute path to the location of the file.
For example: C:\my_data\rasters\canada.dem
The extension needs to be .dem
5) Hit the Submit button and save.
6) Next head over to the Config->Data->Coverages->New menu:
Select your coverage store and hit the New button.
7) You will now be in the Coverage Edit page. It will know your projection, so all you have to do it hit the Submit button at the bottom, then apply and save the changes.
You should now have your Gtopo30 raster image registered in GeoServer.
