JavaScript is currently disabled, this site works much better if you enable JavaScript in your browser. Institute of Policy and Planning Sciences, University of Tsukuba, Tsukuba 305-8573, Japan (e-mail: osawa@sk.tsukuba.ac.jp, koshizuk@sk.tsukuba.ac.jp) Institute of Policy and Planning Sciences, University of Tsukuba, Tsukuba 305-8573, Japan (e-mail: osawa@sk.tsukuba.ac.jp, koshizuk@sk.tsukuba.ac.jp) When demand points are given as a planar map where projection method is explicitly stated, we usually know the latitudes and longitudes of these points from the map. Then we can solve the Weber problem on the globe, and we do not suffer from errors. This paper analyses how cylindrical projections cause distortion in the Weber problem when demands are distributed on the Northern Hemisphere. First, we demonstrate that planar solutions are always located south of the spherical solution if the Mercator projection, the equirectangular projections with standard parallels near the demands, or the equal-area projection with the same characteristic is chosen. Second, we verify that this geographical tendency is inclined to hold when the demand points, are distributed symmetrically, widely or toward the north. This paper was partially written while the first author was visiting the Department of Geography at the Catholic University of Louvain, Louvain-la-Neuve, Belgium [1993–1994]. He is grateful for the hospitality of this department. An earlier version of this paper was presented in 1994 at the Seventh Meeting of the European Operational Research Working Group on Locational Analysis in Brussels, and in 1996 at the Fifth World Congress of the Regional Science Association International in Tokyo. The authors would also like to thank the participants as well as three anonymous referees for their constructive comments. Institute of Policy and Planning Sciences, University of Tsukuba, Tsukuba 305-8573, Japan (e-mail: osawa@sk.tsukuba.ac.jp, koshizuk@sk.tsukuba.ac.jp), JP Source.