A lot has defined boundaries (or borders) which are documented somewhere, but the boundaries need not be shown on the land itself. Most lots are small enough to be mapped as if they are flat, in spite of the curvature of the earth. A characteristic of the size of a lot is its area. The area is typically determined as if the land is flat and level, although the terrain of the lot may not be flat, i. e, the lot may be hilly. The contour surface area of the land is changeable and may be too complicated for determining a lot's area.