Introduction to Map Use

study outline – area measurements

You should be able to:

1. measure area on a map using geometry or a dot grid

2. use the scale to convert an area measured on the map to real world units

3. convert between real world area units

A. area on the map

1. geometry – divide the area to be measured into regular shapes that can be measured with geometry (triangles, rectangle etc.)

2. dot grid – count the dots within the area to be measured, multiply by the area each dot represents

B. scale – both sides of the scale must be squared to use a scale to measure area!

1. examples:

i. 2 in = 5 mi distance scale à 2² in² = 5² mi² area scale

ii. 1:24,000 à 1²:24,000²

C. area units

1. area is sometimes measured in distance units squared

i. to convert between these distance units you must square the linear relationship

ii. 1 in = 12 ft à 1² in² = 12² ft²

2. area is sometimes measured in special area units – acres, ares, hectares

i. use the relationship between squared distance units and area units to convert: 1 mi² = 640 acres

ii. relationships between area units do not need to be squared. 1 ac = .405 ha

D. percent cover

1. visual estimation by fraction of total area

2. dot grid – dots on feature/dots in total area X 100%