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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?