On political maps, physical features are usually shown as gray relief shading. This shading depicts surface features such as mountains, hills, and valleys. Water features are shown in blue. Solid lines and filled-in areas indicate perennial water features; dashed lines and patterns indicate intermittent features. Boundaries and political divisions are defined with both lines and colored bands; they vary according to whether a boundary is internal or international. Corncerning cities, many regional political maps depict four catergories of cities or towns. The largest are frequently shown in all capital letters (e.g., LONDON).