Answer:
1 in = 500 km
Step-by-step explanation:
It is nice to choose a scale that leaves a little border, so one could probably make it ...
10 in = 5000 km
1 in = 500 km
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If you'd rather have a "nice" ratio, you could use ...
2.5 cm = 500 km ⇒ 1 : 20,000,000
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Additional comment
An inch is 2.54 cm, so using 2.5 cm for the same distance means the map is slightly smaller. It would end up about 9.8 inches wide, leaving a border of almost 0.6 inches on either side.
You might want a scale that makes it easy to draw using the tools you have. If your distances are in km, and you have an inch ruler, then the first choice might be better. If you have a centimeter ruler, then the second scale might work better for you.
The unitless scale is found by doing the division:
[tex]\dfrac{2.5\times10^{-2}\text{ m}}{5.00\times10^5\text{ m}}=\dfrac{1}{2\times10^7}=\dfrac{1}{20,000,000}[/tex]
