Grade 9 GeographyMapping Skills – Map Scale

Maps are very useful tools for locating things, determining direction or calculating distances.

What? How do you calculate a real or actual distance from a paper map?

Grade 9 GeographyMapping Skills – Map Scale

Calculating real distances…

You need two things from your map AND a mathematical formula to determine real distances:

• Map Distance – The measured distance on the map

• Scale – A ratio (i.e., each centimetre on the map is how far in real life

• Formula – MD/GD = scale where GD is Ground Distance (the real or actual distance)

Grade 9 GeographyMapping Skills – Map Scale

Map Distance (MD)

With a ruler, you need to measure the distance ON THE MAP from your starting point to your finishing point.

The example shows a trip starting in Istanbul and finishing near the border with Iran. With a ruler, measure the line. This is the distance on the map or Map Distance (MD)

Grade 9 GeographyMapping Skills – Map Scale

Scale

Scale is located on the map…usually along a bottom edge

Scale is a statement of the relationship between distances on a map (i.e., Map Distance (MD)) and distances in real life (i.e., Ground Distance (GD)).

As you know, a drawing made according to the scale will be an exact copy of the real object…only smaller.

Scale is always presented as a ratio on a map. For example, scale is given as 1:25,000,000 which means 1 cm on a map is 25,000,000 cm in real life (or 250 km)

Grade 9 GeographyMapping Skills – Map Scale

Formula

The formula for calculating the real distance (i.e., Ground Distance (GD)) is a ratio.

If you know Map Distance (MD) and scale, you can “somehow” combine them to calculate GD.

MD / GD = scale

Grade 9 GeographyMapping Skills – Map Scale

Example

Scale is 1:37,000,000 or 1 cm = 370 km or 1 / 370

MD = 10.2 cm

What is Ground Distance (GD)?

MD / GD = 1 / 370

Let GD = x

10.2 / x = 1 / 370

x = (10.2)(370) = 3,374

The Ground Distance is 3,374 km

MD / GD = scale

Grade 9 GeographyMapping Skills – Map Scale

Try one

Scale is 1:25,000,000 or 1 cm = 250 km or 1 / 250

MD = 13.2 cm

What is Ground Distance (GD)?

MD / GD = 1 / 250

Let GD = x

The Ground Distance is 3,300 km …right?

MD / GD = scale