Introduction to Map Use

study outline – scale

You should be able to:

1. describe the three different representations of the scale and tell their advantages and disadvantages

2. given a scale in one form, present the scale in either of the other forms

3. given two maps or scales, tell which has the larger scale and which has the smaller scale

4. determine the scale of a map by comparison with another map of the same area with a known scale

5. determine the scale of a map by comparison with measurement of features in the real world

A. definition – the scale of a map the relationship between distances in the real world and distances on a map

B. representations – scales can be represented in three basic ways

1. words

i. definition -- presents the scale in terms of the specific measurement units on the map and in the real world

ii. examples -- 1 inch = 2 miles, 2 cm per kilometer

iii. properties

(1) usually presented as the number of real world units in an easy to use map measurement 1 in or ½ in or 1 cm on the map = 10 miles or meters or feet in the real world, not 1.54 in = 10000 mi.

iv. advantages

(1) presents the scale in terms of common and easy to understand units

(2) makes using a ruler to convert ruler measurements on the map to distances in the real world easy

(3) makes visual estimation of distances easy

v. disadvantages

(1) not meaningful to people unfamiliar with the units (English or metric)

(2) not valid if the map is enlarged or reduced

2. fraction or ratio

i. definition – presents the scale as the relationship between distances measured in the same units on the map and in the real world

ii. examples -- 1/24000, 1:1,000,000

iii. properties

(1) always presents the scale as 1 unit on the map equals X units in the real world

iv. advantages

(1) can be used with any units

(2) allows easy comparison between maps

v. disadvantages

(1) not valid if the map is enlarged or reduced

(2) requires working with large numbers and multistep calculations to move back and forth between the map and the real world

3. graphic

i. definition – presents the scale as a line on the map that represents a specified distance in the real world

ii. example – 1000 ft

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iii. properties

(1) should represent an easy to use, round number of real world units

(2) often shows subdivisions of the distance e.g. 1000 ft with a mark every 100 ft

iv. advantages

(1) valid if the graphic is enlarged or reduced with the map

(2) makes measurements with just a paper straight edge easy

v. disadvantages

(1) harder to use accurately than the other scales

(2) hard to use to measure long distances

C. calculation and conversion

D. scale

1. scale calculation

i. technique

(1) map:ground

(2) simplify

ii. examples

(1) odometer

(2) football field

(3) text to ratio 1” = 1 mi. => 1:63360

(4) ratio to text

(5) ratio to text 1: 40,000 => 1” = 3333 ft 1111 yd .63 mi ~1 km

E. scale comparison – a scale is called small, intermediate or large depending on the size of the scale fraction

1. large > 1/50,000 streets and houses, part of a city

2. intermediate > 1/50,000 to 1/250,000 whole town to whole city layout

3. small > 1/250,000 roads and city location, large scale geology

no universal definition – more comparative