images are tiled as 4 kilometer squares, according to the Orthophoto Index , rather than by the original 7.5-minute sheets used by the U.S. Geological Survey for its paper map versions.
When downloading these Quad images, you will need to select the 4km-square images that cover the extent of the original paper map. In the example at right, in order to view all images for the Shelburne Falls quad (as it was tiled as a paper map), one would need to download 15 individual images (as well as their header files - .tfw for TIFF and .sdw for MrSID), as indicated by the 6-digit IDs. In this example, the TIFF images would be named q101930.tif, q105930.tif, etc.
To best determine the tiles you need:
- refer to the Scanned USGS Topographic Map Images Reference , a .PDF file (viewable in the free Adobe Acrobat Reader) that displays the original USGS paper map scheme and MassGIS' image tiling index. Town names and boundaries are also included.
- download a .dbf file that lists the corresponding OQ IDs for each town. This file may be displayed in any program that supports dBASE format, such as ArcGIS, Excel, and others.