Terrain - Aspect

This layer provides aspect values calculated dynamically using the server-side aspect function applied on the Terrain layer. The values are float, and represent the orientation of the downward sloping terrain in degrees (0 to 360), clockwise from north. Cells in the input raster that are flat with zero slope are assigned an aspect of -1. Units: Degrees Update Frequency: Quarterly Coverage: World/Global Data Sources: This layer is compiled from a variety of best available sources from several data providers. To see the coverage and extents of various datasets comprising this service in an interactive map, see World Elevation Coverage Map. WARNING: Aspect is computed in the projection specified by the client software. The server resamples the data to the required projection and then computes aspect. The default projection for web applications is Mercator in which scale increases equally in x and y by latitude, so aspect computations are not affected. Using geographic coordinates will give distorted results. It is advised to check the client application projection prior to obtaining aspect values. What can you do with this layer? Use for Visualization: No. This layer provides numeric values indicating terrain characteristics, and is not generally appropriate for visual interpretation, unless the client application applies an additional color map. For visualization use the Terrain - Aspect Map. Use for Analysis: Yes. This layer provides numeric values indicating the orientation of the terrain within a raster cell, calculated based on the defined cell size. There is a limit of 5000 rows x 5000 columns. For more details such as Data Sources, Mosaic method used in this layer, please see the Terrain layer. This layer allows query, identify, and export image requests. The layer is restricted to a 5,000 x 5,000 pixel limit in a single export image request. This layer is part of a larger collection of elevation layers that you can use to perform a variety of mapping and analysis tasks.

本图层提供基于服务端坡向（aspect）函数对地形（Terrain）图层进行动态计算得到的坡向值。该值为浮点型数据，表示向下倾斜地形的朝向，单位为度（取值范围0至360），以正北为基准顺时针计算。输入栅格（raster）中坡度为0的平坦区域，其坡向值被赋值为-1。
单位：度
更新频率：季度
覆盖范围：全球
数据源：本图层由多家数据服务商提供的各类最优可用数据源整合而成。如需在交互式地图中查看组成该服务的各类数据集的覆盖范围与范围边界，请访问「全球高程覆盖地图（World Elevation Coverage Map）」。
警告：坡向（aspect）的计算基于客户端软件指定的投影坐标系。服务端会先将数据重采样至所需投影坐标系，再进行坡向计算。Web应用的默认投影为墨卡托（Mercator）投影，该投影下尺度随纬度在x、y轴上均匀增加，因此坡向计算不受影响。若使用地理坐标系进行计算，则会得到畸变的结果。建议在获取坡向值前，先确认客户端应用所使用的投影坐标系。
本图层可用于哪些场景？
可视化应用：否。本图层仅提供表征地形特征的数值数据，通常不适用于直接视觉解译，除非客户端应用额外应用了色彩映射表。如需可视化展示，请使用「地形-坡向地图（Terrain - Aspect Map）」。
分析应用：是。本图层提供表征栅格单元格内地形朝向的数值数据，其计算基于预设的单元格尺寸。单次请求的栅格尺寸上限为5000行×5000列。
如需了解更多细节（如数据源、本图层所采用的镶嵌方法），请参阅地形（Terrain）图层。
本图层支持查询、识别以及影像导出请求。单次影像导出请求的像素尺寸上限为5000×5000。
本图层属于高程图层集合的一部分，可用于开展各类制图与分析任务。