Draw a plain scale for a map whose scale is 1 inch : 7 miles.

 1 inch represents a distance = 7 miles

6 inch represents a distance = 7 × 6 = 42 miles

But 42 miles is not a round number. Select a round number of 45 miles. Find out the map distance for a distance of 45 miles.

7 miles are represented by = 1 inch

1 mile is represented by = 1/7 inch

45 miles are represented by = 1/7 × 45

= 6.4 inches approximately.

Scale 1 Inch: 7 Miles

Construction. Draw a line 6.4 inches long. Divide it into nine equal parts. Each part showing 5 miles. Sub-divide the left-hand part into 5 divisions, each will show a distance of 1 mile.