Set out the map on a flat surface and find the legend. The legend is the "code" of the map and includes the scale. Scales are the distance on the map as related to actual distance. For example, a 1:100 map means that every one unit on the map represents 100 actual units of measurement. Typical distance measurements in North America are in miles and kilometers. Locate your method of measurement on the map.
Place the ruler along the proposed route and measure the road distances. If the map is in metric, use centimeters; if in imperial, use inches. Since you are going for an estimation do not get too concerned with getting every curve measurement. Instead, go for a rough distance between the beginning and the end of the journey.
Add the measurements for a sum. For example, if you measured three different legs at 12, 14, and 16 inches, add them for a total of 42.
Multiply the sum of the measurements by the scale of the map. For example, if the scale is 1:10, and the sum is 42, multiply 42 by 10 for a total of 420. If the map is in kilometers, the distance is 420 km; or if in miles, it is 420 miles.
Program a GPS unit to provide road distance by inputting the departure and arrival address and pressing the calculate function.
