Digital Elevation Model (AZ 250,000:1)

1:250000 scale Digital Elevation Model of Arizona. Digital Elevation Model (DEM) is the terminology adopted by the USGS to describe terrain elevation data sets in a digital raster form. The standard DEM consists of a regular array of elevations cast on a designated coordinate projection system. The DEM data are stored as a series of profiles in which the spacing of the elevations along and between each profile is in regular whole number intervals. The normal orientation of data is by columns and rows. Each column contains a series of elevations ordered from south to north with the order of the columns from west to east. The DEM is formatted as one ASCII header record (A-record), followed by a series of profile records (B-records) each of which include a short B-record header followed by a series of ASCII integer elevations per each profile. The last physical record of the DEM is an accuracy record (C-record). A 30-minute DEM (2- by 2-arc second data spacing) consists of four 15-by 15-minute DEM blocks. Two 30-minute DEM's provide the same coverage as a standard USGS 30- by 60-minute quadrangle. Saleable units are 30- by 30-minute blocks, that is, four 15- by 15-minute DEM's representing one half of a 1:100,000-scale map.

亚利桑那州1:250000比例尺数字高程模型（Digital Elevation Model, DEM）。数字高程模型（DEM）是美国地质调查局（U.S. Geological Survey, USGS）采用的术语，用于指代数字栅格形式的地形高程数据集。标准DEM由置于指定坐标投影系统下的规则高程阵列构成。DEM数据以一系列剖面形式存储，各剖面内部及剖面间的高程间距均为规整的整数间隔。数据的标准排布方式为行列形式：每一列包含一组由南至北排列的高程值，列的排布顺序则由西向东。DEM的文件格式以一条ASCII头部记录（A记录）为起始，随后接续一系列剖面记录（B记录）；每条B记录均包含简短的B记录头部，其后跟随该剖面的一系列ASCII整型高程值。DEM的最后一条物理记录为精度记录（C记录）。30分幅DEM（数据间距为2×2弧秒）由四个15×15分幅的DEM区块组成。两幅30分幅DEM的覆盖范围与标准USGS 30×60分幅四边形图幅一致。可售卖的单元为30×30分幅区块，即由四个15×15分幅DEM组成的单元，对应1:100000比例尺地图的半幅幅面。