Explain how a map is made. Say that a picture of a neighborhood, city, state or country taken from above can be made into a map. Tell students maps can also be made by traveling and recording the roads and landforms.
Show students a map with a scale on it. If possible blow it up using a projector. Explain that the map scale expresses the relationship of distance on the ground to distance on the map. For example, on a California road map, one inch on a map might represent 80 miles on the ground.
Show how to find a distance on a copy of state map with a map scale on it. Pass out maps and rulers to each student. Find two cities where you can measure the distance in inches on the map. For example, on a California map choose San Francisco to San Jose, a distance of about 45 miles.
Demonstrate with a ruler how you can estimate the distance between the two cities while the students follow along. For example, on the California map tell students to place the beginning of the ruler on the dot that shows San Francisco, and measure in inches how far San Jose is. The answer will be a little more 1/2 inch. Explain to students that since one inch on the map is 80 miles on the ground, then 1/2 inch is about 40 miles. Then explain since it's a little over 1/2 inch the answer is between 40 and 50 miles.
Have students measure how far it is from one city to another with a ruler and estimate what the distance would be on the ground, using the value given on the map scale to calculate it. For example, students could use the process explained in the example of Step 4 to find the distance between San Francisco and Los Angeles, Eureka to South Lake Tahoe and other pairs of cities.