Acquiring  GIS  Data: Utah

Vertical relationship of Index files:

For a further understanding and breakdown of the various quadrangles let’s look at the next graphic, which combines the above index files and shows the relationships between them.  

Results: ( Quads_30x60_1x2 )

Each blue line is labeled with the appropriate latitude or longitude value, as well as the two crossing red lines.  Notice that there is 1 degree difference between the top blue line and the bottom blue line, yet between the left and right blue lines there are 2 degrees.  The area inside the blue lines make up the 1:250k or 1 x 2 degree quadrangle area.  Within the 1:250k areas there are four 1:100k quadrangles known as 30’ x 60’ or 1 degree x 30 minute quadrangles, each 1:100k area is 1 degree east and west and 30 minutes north and south.  Within each 1:100k area there are thirty-two 7-1/2’ quadrangles that form an 8 x 4 matrix. 

If we do the math, 4 x 7-1/2’ = 30’ and 8 x 7-1/2’ = 60’, thus we have a 30’x 60’ area.  By understanding this relationship and knowing the requirements for your project, you will be able to decide how much time and effort you will need for data collection.     

For additional comparison of ground cover of each index their and relationships see the Digital Raster Graphs (DRG) example that was used above:

Results: ( scale_24_100_250 )

Questions:

Why are the 1:24k quads called 7-1/2’ quads?

How many 7-1/2’ quads make up a 1:100k quad area?

How many 7-1/2’ quads in a 1:100k quad area in the N-S direction, W-E direction?

How many 100k quads make up a 1:250k quad area?

Why are the100k quads sometimes called a 30x60?

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