Estimate error tolerance Chapter 7
In this exercise, you will see the relationship between map scale, minimum size of the mapped area, and error tolerance. You will go through the process of using error tables to determine the error tolerance, given the map scale and minimum area requirements for creating the requested information product.

Step 1  Determine minimum area to be mapped 
 The parks and recreation staff in your city are looking for a 25acre site for a minor league baseball field and stadium.
What is the minimum size of the parcel in hectares that needs to be mapped? (2.471 acres = 1 hectare) Answer The minimum size of the parcel that needs to be mapped is 10 hectares (25 divided by 2.471 acres is approximately 10).

Step 2  Identify map scale 
 Your city has three source maps for you to use: Parcels, Park and Recreation Facilities, and Slope. The map scale of the Parcels map is 1:5,000, the map scale of the Park and Recreation Facilities map is 1:24,000, and the map scale of the Slope map is 1:24,000.
Which source map will most accurately show the smallest areas? Answer The Parcels map will most accurately show the smallest areas because it has the largest map scale (1:5,000).
What scale will you need to identify possible sites for the baseball field? Answer You will need to identify possible sites for the baseball field at a scale of 1:5,000, since the parcels define the smallest area to map.

Step 3  Determine the appropriate error table to use 
 Review the two error tables below.
Which error table should you use to find sites for the baseball field? Answer Knowing the area you need for the baseball field and the map scale, you can use the "Percent error in area measurement for a given area and map scale" table.

Step 4  Estimate error tolerance 
 Using the table you chose in step 3, estimate the error tolerance for the maps of the proposed baseball stadium sites.
What is the estimated error tolerance? Answer The estimated error tolerance for the maps of the proposed baseball stadium is 1.7 percent (the intersection of 10 hectares and 1:5,000 is 1.7). 