Grade 9 Geography
Mapping 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 Geography
Mapping 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 Geography
Mapping 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 Geography
Mapping 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 Geography
Mapping 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 Geography
Mapping Skills – Map Scale
MD / GD = 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
Grade 9 Geography
Mapping Skills – Map Scale
MD / GD = 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?