ArcView Tutorial 2: Creating Access Maps

Adding and Editing DRG's

DRGs are Digital Raster Graphics and are scanned copies of USGS maps.   You will add DLGs to the project file with the add theme button , but in this case you will have to change the "Data Source Types:" drop box to "Image Data Source."  A thumbnail of a DRG (converted to jpg) is linked below.  DRGs are very useful as a background for the rest of your data, be it land status or trail and site easements.  By holding down the shift key and clicking on each TIF you can select several at a time .. add all of them.  Select and activate one DRG and inspect the image.   Zoom to selected theme .  For ease of viewing you must remove the green forest color and also remove the black "collar" that is around the DRG (due to the elliptical shape of the earth, DRG's aren't oriented exactly square in the northern and southern reaches of the hemispheres).  You will perform this action by 2x each DRG theme and then clicking the Colormap button, at which point the Image Colormap dialog box will appear.  2x the white box on number 1 (highlighted in the image at left) and click the x'd box (upper left corner) in the Color Palate, then apply. Repeat this procedure for number 5 (the green forest) and number 255 (the black collar around the DRG).  You may have to repeat this process for number 1, or click on a color and then the x'd box .. I'm not sure why, but it sometimes just doesn't work the first time.  You must repeat this process for each DRG you add.

One thing to consider: at times 1:250,000 DRGs are just as useful as 1:63,360s and don't take as long to load (if you have a large area).  Also, when you are editing other layers (such as land status) that do not require the DRG to be seen and the redraw time is rather lengthy, turn off the DRGs for quicker turnaround.  This is also true for the sections, townships, or any other large theme.

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