This paper proposes a method for determining the size of map labels from a statistical view. Though larger letters are more readable than smaller ones, they sometimes cause the overlaps of letters, and thus it may leads the inefficiency of GIS operations. In this paper, we show two indices for evaluating the readability of map labels: visible letter area and readable letter area. The former is the area of rectangles in computer display which include letters of map labels. The, latter is also the summed area of rectangles, though it excludes over-lapped rectangles. These indices arecalculatedin several cases, and we show the relationship between these indices and the size of letters. We, can:thuscexpect the area of overlapped letters statistically, and control it by adopting letters of proper'size. This methodhis applied to the names of stations in Yokohama, and some empiri-cal findings are shown.