250k USGS Quadrangle Boundaries

Most USGS topographic maps use brown contours to show the shape and elevation of the terrain. Contour intervals vary, depending mainly on the type of terrain and the scale of the map. (Scale is the relationship between distance on the map and distance on the ground.) In the 1:250,000 series, quadrangles are 1 degree of latitude by 2 degrees of longitude. Along the coasts dimensions are modified to fit some maps. The series consists of 489 sheets. Ground area shown varies with latitude, from 8,218 square miles at 30 degrees north to 6,222 square miles at 49 degrees north. Sheet size is about 32 x 22 inches. About 8 percent of these sheets have been replaced by folded metric maps, about 36 x 22 inches in size.绝大多数美国地质调查局（USGS）的地形地图均采用棕色等高线来呈现地表形态与海拔高程。等高距并非固定值，主要取决于地形类型与地图比例尺（比例尺即地图上距离与实地距离的比例关系）。在1:250000比例尺系列中，标准图幅的范围为1个纬度跨度与2个经度跨度；沿海区域的部分地图会调整图幅尺寸以适配制图需求。该系列总计包含489幅图幅，单幅图涵盖的实地面积随纬度变化：北纬30°处约为8218平方英里，北纬49°处则缩减至6222平方英里。单幅图的尺寸约为32×22英寸，其中约8%的图幅已被折叠式公制尺寸地图替代，此类替代地图的尺寸约为36×22英寸。