1. A process comprising: receiving, by one or more computing devices, first data representing a first polygon having a first set of vertices; generating a resulting polygon at least in part by: using polygon expanding logic of the one or more computing devices, causing determining a second polygon having a second set of vertices, such that the second polygon encompasses the first polygon, by determining, for each particular vertex in the first set of vertices, one or more new vertices that are determined from that particular vertex and are at least a particular distance outside the first polygon; using vertex reducing logic of the one or more computing devices, causing determining, for an intermediate vertex of the second set of vertices, whether the intermediate vertex is within the particular distance of a proposed segment between two other vertices of the second set of vertices, wherein the intermediate vertex is not on the proposed segment; using the vertex reducing logic, causing removing the intermediate vertex from the second set of vertices in response to determining that the intermediate vertex is within the particular distance of the proposed segment; on one or more non-transitory computer-readable storage media, storing the resulting polygon in association with the first polygon, wherein the resulting polygon has fewer vertices than the first polygon.