The application of astronomical concepts and the extension of the knowledge of the world through exploration encouraged attempts to map the known world Then astronomers discovered that the earth is not a perfect sphere but is flattened slightly at the poles which introduced further refinements into the mapping of large areas Meanwhile the demands being made of the map maker were shifting significantly The traveller or the merchant ceased to be the sole user of maps The soldier especially after the introduction of artillery and the problems of range field of fire and dead ground which it raised demanded an accurate representation of the surface features in place of the earlier conventional or pictorial delineation and a solution in any degree satisfactory was not reached until the contour was invented