equations (a) and (b) respectively gives For the projections other than Mercator we must first calculate from and using equation (c), before we can find . For example, the equirectangular projection has so that If we consider a line of constant slope on the projection both the corresponding value of and the scale factor along the line are complicated functions of . There is no simple way of transferring a general finite separation to a bar scale and obtaining meaningful results. Ratio symbol While the colon is often used to express ratios, Unicode can express a symbol specific to ratios, being slightly raised: . See also Geographic distance Scale (analytical tool) Scale (ratio) Scaling (geometry) Spatial scale References Cartography Chinese inventions Measurement