DIGITAL RASTER GRAPHICS (DRGs): 7.5-MINUTE TOPOGRAPHIC MAPS

Status

There is complete statewide DRG coverage for North Carolina; a complete table is listed below. Complete statewide coverage was achieved in September 1997. The DRGs are available on CD-ROMs in TIFF format. Most CD-ROMs contain 64 --7.5-minute quadrangles; some contain only 32 -- 7.5-minute quadrangles because of production quirks. In addition, each CD-ROM contains corresponding 1:100,000 (100K) and 1:250,000 (250K) sheets.

The cost is $7.55 plus state tax (for orders destined to NC addresses) per CD-ROM (total of $8.00). There is a nominal charge for shipping and handling. The price is subject to change. The base price is based on reproduction costs. There are no discounts for multiple CD orders or for government agencies.

Use the following index to help address specific questions you may have:

• Purchasing DRGs
• About digital raster graphics (DRGs)
• DRGs for the following areas are available
• Ordering information
• FAQ about using DRG data from CD-ROM

For additional suggestions on the use of DRGs and other digital products, a GIS information page was created. Through links on that page, additional technical information are available.

Purchasing DRGs

The NC Geological Survey carries DRGs. Purchase is "over the counter," by mail. Credit cards (MasterCard and Visa) are now accepted for CD-ROM purchases. You may call (919) 715-9718, send a facsimile to (919) 733-0900 for additional information. You may also contact us by e-mail at: tonya.merritt@ncmail.net

The cost is $7.55 plus state tax (for orders destined to NC addresses) per CD-ROM (total of $8.00). There is a nominal charge for shipping and handling. The price is subject to change. The base price is based on reproduction costs. There are no discounts for multiple CD orders or for government agencies.

Credit card orders (MasterCard and Visa) for this product are now accepted. Cash, checks and money orders are accepted. Journal 10 orders for state agencies are accepted also. All orders must be prepaid. Please allow one week for delivery.

Place orders by block number as described below. You may request a page-sized paper map showing these blocks.

About Digital Raster Graphics (DRGs)

• A digital raster graphic (DRG) is a scanned image of a 7.5-minute topographic map (or related maps). The scanned image includes all map collar information. The image inside the map neatline is georeferenced to the surface of the earth. The DRG can be used to collect, review, and revise other digital data, especially digital line graphs (DLGs). When the DRG is combined with other digital products, such as digital orthophoto quarter-quadrangles (DOQQs) or digital elevation models (DEMs), the resulting image provides additional visual information for the extraction and revision of base cartographic information.

• The first step in the process is to scan a paper 7.5-minute topographic map (or related map). Scanning a standard 7.5-minute quadrangle at a resolution of 500 dots per inch results in a red-green-blue (RGB) file of up to 300 megabytes. The RGB file is converted into tagged image file format (TIFF), viewed, and the position of each of the sixteen 2.5-minute grid ticks on the image is collected. Software uses these coordinates to rectify and georeference the image to the UTM ground coordinates. A precise linear transformation completes the georeferencing.

• The DRGs are generally packaged in 1-degree x 2-degree blocks in TIFF format on a CD-ROM; several are in 30x60 minute (1:100,000-scale blocks) because of production quirks. Generally the CD-ROM contains: 64 7.5-minute quadrangles, two 1:100,000-scale maps, and the appropriate 1:250,000-scale map(s) -- see below.

DRGs for the following areas are available:

For further information

Order DRGs through our sales office

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