Determine map scale  Chapter 7
In this exercise, you will again examine the relationship between map scale, minimum area to be mapped, and error tolerance. You will use error tables to determine the map scale, given the error tolerance, and minimum area requirements for producing the requested information product.

Step 1  Determine minimum area to be mapped 
 One of your information products is a statewide map showing water bodies. The map needs to show lakes larger than 25 acres, reservoirs larger than 25 acres, and playas larger than 50 acres.
What is the minimum size water body in hectares that needs to be mapped to create this information product? Answer The minimum size water body that needs to be mapped is 10 hectares—25 divided by 2.471 is approximately 10.

Step 2  Determine percent error in area 
 The information product description for the statewide water body map requires that the area of the water bodies being mapped needs to be accurate to within +/ 1 hectare.
Using the minimum area to be mapped from step 1, determine the percent error in area that is acceptable.
What is the acceptable percent error in area? Answer The percent error in area that is acceptable is 10 percent—1 hectare is 10 percent of 10 hectares, the minimum area to be mapped.

Step 3  Determine which error table to use 
 Review the two error tables below.
Which table should you use to find the appropriate scale for mapping the water bodies? Answer Since you know the area needed for the water bodies and the error tolerance, you can use the "Map scale for a given area and error tolerance" table.

Step 4  Determine the map scale 
 Using the table you chose in step 3, determine the smallest map scale to produce the water bodies information product.
What is the smallest map scale that should be used? Answer The smallest map scale that should be used for the water bodies information product is approximately 1:30,000 (the intersection of 10 hectares and 10 percent error tolerance is 30,117). Scales larger than 1:30,000 could also be used, so the widely available 1:24,000 topographic maps would be suitable. 