A cost zone about an origin on a digital map includes the area on the map that can be traveled to, from the origin, which has a cost of travel less than a predetermined cost. The cost can be measured in distance, time of travel, ease of turning, tolls, etc. The steps of creating a cost zone include identifying a set of decision points on the map that are within a predetermined factor of the desired cost, triangulating the decision points to create a set of triangles and interpolating along a subset of the sides of the triangles to estimate the locations along the sides that can be traveled to at the desired cost.
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