Digital Elevation Model (AZ 7.5 - Minute)

7.5 Minute Digital Elevation Model for the state 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). The DEM for 7.5-minute units correspond to the USGS 1:24000 scale topographic quadrangle map series for all of the United States and its territories. Each 7.5 minute DEM is based on 30- by 30-meter data spacing with Universal Transverse Mercator(UTM) projection. Each 7.5- by 7.5-minute block provides the same coverage as the standard USGS 7.5-minute map series.亚利桑那州7.5弧分数字高程模型（Digital Elevation Model, DEM）。数字高程模型（Digital Elevation Model, DEM）是美国地质调查局（United States Geological Survey, USGS）所采用的术语，用于描述以数字栅格形式存储的地形高程数据集。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数据以一系列剖面的形式存储，每个剖面内部及剖面之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：每一列包含一系列从南到北排列的高程值，而列的整体排布顺序则为从西到东。该DEM的文件格式为：先包含一条ASCII格式的头记录（A记录，A-record），随后是若干剖面记录（B记录，B-records）；每条B记录均带有一段简短的B记录头信息，其后跟随该剖面对应的一系列ASCII整数高程值。DEM的最后一条实体记录为精度记录（C记录，C-record）。7.5弧分单元的DEM与美国本土及所有海外领地的美国地质调查局（USGS）1:24000比例尺地形四边形图幅系列一一对应。每幅7.5弧分DEM均采用30米×30米的空间分辨率，基准投影为通用横轴墨卡托（Universal Transverse Mercator, UTM）投影。每幅7.5弧分×7.5弧分的图块，其覆盖范围与标准USGS 7.5弧分地形图系列完全一致。