Aspect Analysis
Aspect analysis determines the compass direction that each cell of a terrain surface faces, measured as an azimuth from 0 to 360 degrees. It is essential for understanding solar exposure, vegetation distribution, snowmelt patterns, and microclimate variation across landscapes.
Aspect analysis is a terrain derivative that calculates the downslope direction of the maximum rate of change in elevation for each cell in a digital elevation model (DEM). The result is a raster surface where each cell value represents the compass direction (azimuthAzimuthAzimuth is the angular measurement of direction from north, measured clockwise in degrees from 0° to 360°. It is a fu...) the slope faces, typically measured clockwise from north (0/360 degrees) through east (90), south (180), and west (270). Flat areas with no slope are commonly assigned a value of -1.
Calculation Method
Aspect is computed from a DEM using a 3x3 moving window that calculates the partial derivatives of elevation in the east-west (dz/dx) and north-south (dz/dy) directions. The aspect angle is then derived as the arctangent of the ratio of these derivatives. Common algorithms include the Horn method and the Zevenbergen-Thorne method, both available in standard GISGISGeographic Information Systems (GIS) enable users to analyze and visualize spatial data to uncover patterns, relation... software. The result is typically classified into eight cardinal and intercardinal directions (N, NE, E, SE, S, SW, W, NW) or displayed as a continuous surface.
Applications
Agriculturists and foresters use aspect to understand solar exposure patterns that affect crop growth, timber productivity, and irrigation needs. South-facing slopes in the Northern Hemisphere receive more direct sunlight, influencing vegetation type and density. Hydrologists combine aspect with slope to model snowmelt timing and runoff direction. Real estate analysts assess property solar exposure for energy efficiency evaluations. Ecologists map aspect to understand habitat microclimates and species distribution patterns.
Relationship to Other Terrain Derivatives
Aspect is closely related to slope analysisSlope AnalysisSlope analysis calculates the steepness or gradient of terrain at each location from digital elevation data, producin... (which measures steepness) and hillshadeHillshadeHillshade simulates the illumination of a terrain surface by a hypothetical light source, creating a shaded relief im... (which uses aspect and slope to simulate illumination). Together, these terrain derivatives provide a comprehensive characterization of surface morphology essential for terrain modeling and landscape analysis.
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