map scale

Variable Scale Bar

(used on a Mercator map where scale varies systematically from north to south)

numeric scale

A ratio of the map distance to the ground measurement in the real world It is always written as 1/x or 1:x The numerator represents map distance It is always equal to 1 The denominator represents ground distance in the same units as the numerator

If you want inches to 1 mile then divide 63360 by the denominator of the R.F.

Ex. Convert an R.F. of 1:200000 to inches per 1 mile (63360 in/mile) / 200000 in = (63360/200000) in = 1 mile 0.32 inches = 1 mile

Verbal Scale

Expresses the large denominator of the Representative Fraction in a unit that is more familiar Ex. A R.F. of 1/24000 can be expressed as "1 inch to 2000 feet" Ex. A R.F. of 1:100000 Can be expressed as 1 cm to 1 km Verbal scales are usually approximations

Verbal Scale to R.F.

Step 1 - set up a ratio Step 2 - put into the same units Step 3 - reduce the fraction to the form 1/x and cancel units

Using Fractional Scales to Compute Distance

Step 1: Use a ruler to measure the distance on the map Step 2: Multiply the measured distance by the denominator of the fractional scale to get actual distance Step 3: Convert your calculated distance to a useful unit We have a map with scale 1:50000 We measure a distance on the map of 25 centimeters 25 cm X 50000 = 1250000 cm 1250000 cm X (1 m / 100 cm) = 12500 m 1250000 cm X ( 1 km / 100000 cm) = 12.5 km

Ex. Given the verbal scale 3 inches to 10 miles what is the R.F. ?

1. 3 inches : 10 miles 2. 10 miles x 63360 inches/mile = 633600 inches 3. 3 inches : 633600 inches 4. 1 inch : 211200 inches 5. 1:211200

Some handy numbers to remember

12 inches per foot 5280 feet per mile 63360 inches per mile 100000 centimeters per kilometer 1000 meters per kilometer 1 inch per 2.5 cm

Large Scale vs Small Scale

Think about division 1/1000 = .001 Shows small area Shows more detail 1/1000000 = .000001 Shows large area Shows less detail