Help: Import Grids
You may view a tutorial movie demonstrating how a .grd file is imported (requires Flash).
To import a gridded dataset in GMT’s netCDF .grd format go to the File menu and select Import Grid.
Choosing Browse Your Disk allows you to choose the type of grid you would like to search for.
The Open window will then open and allow you to browse your computer for the type of grid file you selected previously. A mosaic formed of many gridded files can be imported together as a single shapefile by placing all the .grd files in a single directory (folder) and selecting them all at one time. The imported grid is then identified by the name of the directory/folder containing the files. Grids you wish to view individually should each have a separate folder/directory.
Select the grid (or grids) that you wish to import and press Open. A new window, called Confirm projection & Bounds, pops up.
In the Projection drop-down menu, select between Geographic and UTM grid projections. For a UTM grid, select the UTM zone. Hit OK. The grid is now read in to GeoMapApp and is indexed to each of the levels of nested resolution. The progress of this indexing is displayed in the Import Grid window.
When the grid has been indexed, an entry for it appears in the Layers window. If it is not selected, click on the entry to select it. It turns blue.
The grid loads and should automatically zoom to the grid region.
The Layers window allows the user to manage multiple grids and shapefiles. By checking and unchecking the 'visible' boxes, image layers can be turned off and on. Click 
to dispose of a file you no longer wish to view.The info 
button opens a browser window displaying more information about the selected dataset or its source.
The folder
icon opens the list of Available Data so that additional data may be added to your map window.
Click the yellow light bulb 
to bring up the Grid Options (palette tool) window:
Using this tool, you can change the coloring, vertical exaggeration and illumination used in the map window. For more information see Palette Tool.
The imported grid can be colored, illuminated, contoured, profiled, saved, overlain with imported data points, etc., in just the same way as the native GeoMapApp DEM tiles. Note that the imported grid is not merged with the GeoMapApp global DEM tiles – it is a geo-referenced overlay grid.