8.5 Map Spread

Map spread, in inches, is the size of a fire as scaled to a map. See Section 5.3 for more detailed information.

Example 1. For a rate of spread of 4 chains/hour and a projection time of 3 hours, find the map distance for the fire spread. Plot the distance using a tenths ruler for accuracy. The map scale is 1:24,000.

Step 1. Convert the map scale to feet per inch. 24,000 in × 1 foot/12 in = 2000 feet.

Step 2. Convert the spread distance to feet. 12 chains × 66 feet/chain = 792 feet.

Step 3. Convert the ground spread distance to a map spread distance. 792 feet × 1 inch/2000 feet = 0.4 inch

Step 4. Using a ruler, measure the distance from the point of origin to the distance of the fire spread.

Map spread distance is 0.4 inch.