Some of you know this has been a pet topic of mine.

After lots of trial and error, I have a procedure that I'm pretty happy with so I would like to share it. You will need Globalmapper and either Photoshop or Photoshop Elements (could also be done with GIMP I'm sure). The procedure is pretty straightforward but involves a number of steps that I will summarize below.
This tutorial assumes you have some basic knowledge of the NLCD and its color coding scheme, although I will show the exact process that I used.
First you need to download the 2006 NLCD imagery, which is one big file covering the entire US. I suggest you crop this down to a very small area for the purpose of experimenting because processing time can be significant with a large file. For example, one USGS 24k quad is about 500x500 pixels and will process pretty quickly.

This is what you should initially see in Globalmapper.

Right-click the image layer in the Control Center and create area features. This function creates polygons from raster images based on the criteria you specify.

I have decided to only extract two things from the image: forest cover and populated areas. I'll leave it up to you to work out similar techniques for extracting other data. Create a layer called forest using the option for selected colors, then choose the colors shown - Palette ID numbers 1, 3, 4, 5 and 8. These are different kinds of vegetation recognized by the NLCD.

After completing this, use the following options to extract the populated areas (which I will call "residential") - palette ID numbers 11, 12 and 13. I am also creating a new layer called residential for these.

This is what you should now see.

Change the Globalmapper background color to black - this will help isolate the colors in Photoshop.

Select all objects on the residential layer, specify a custom style with a null border and solid fill of primary red (RGB value of 255,0,0).

Repeat this for the forest layer using primary green as the fill (RGB 0,255,0). You should now see something like this

We will now export the results as a TIFF raster image using the following options. I am up-sampling the image in order to create a smoother final result (anti-aliasing). I find that 50 feet/pixel is a reasonable setting for a 24k map but feel free to try other values. Processing time and file size will increase with higher settings, lower settings may look too "jaggy". Also be sure to save a TFW and PRJ file or you will have a problem opening it in Globalmapper after modifying in Photoshop.

(continued in next post)