Using Areal-Scale as Opposed to the Linear-Scale for Map Applications

Abstract

Maps are made to scale. Scale represents the ratio of distance on the map to distance on a projected coordinate system, i.e., Universal Transverse Mercator (UTM). This specification is, however, limited by the fact that different lines produce different scales. This often has disadvantages for users who may require an optimal scale; one scale representing the entire map. Scale variations clearly show that measurements on maps are deteriorated by biases. It is, therefore, desirable to have a unique scale independent of linear measurements to enhance the accuracy of further data processing. In this contribution, an optimal scale based on the relationship between the areas on a map and a reference ellipsoid is proposed to reduce the distortions of the projected coordinate system.The motivation behind the area approach is the fact that as the number of lines approaches infinity on a map, a surface is built which is accurately represented by an area as opposed to linear features. Using several map projections, this paper demonstrates that linear-scale optimization is achieved through areal-scale. Almost all of the commercial software measure the linear-scale based on one line. The linear scale remains unchanged even if the projection is changed or map view moved. Therefore, this contribution can pave the way for GIS industry to present a better indication of scale and more accurate data processing results.