Even if you assume a local mercator projection (centered on your business or whatever) you still need to know that the earth is spherical. Otherwise, you're li

Even if you assume a local mercator projection (centered on your business or whatever) you still need to know that the earth is spherical. Otherwise, you're likely to assume that an 0.1 degree change in latitude is the same distance as an 0.1 degree change in longitude. To correct this erroneous assumption (for small distances) divide your longitude differences by the sine of your latitude.