authority: folia
slug: aspect
name: Aspect
domain: land
subdomain: topography
authority_id: folia:aspect
parent: elevation
external_ids:
  cf_standard_name: null
canonical_units: degree
external_validations:
  gdal:
    tool: gdaldem
    algorithm: aspect
    docs_url: https://gdal.org/programs/gdaldem.html#aspect
  qgis:
    algorithm_id: native:aspect
    docs_url: https://docs.qgis.org/latest/en/docs/user_manual/processing_algs/qgis/rasterterrainanalysis.html#aspect
  gee:
    op: ee.Terrain.aspect
    docs_url: https://developers.google.com/earth-engine/apidocs/ee-terrain-aspect
description: |
  Compass direction the slope faces, expressed as degrees clockwise
  from north (0-360). Flat areas (slope below a threshold) are nodata.
  Same 3x3 neighbourhood as slope; same Horn (1981) algorithm in GDAL,
  QGIS, and Earth Engine. Used by solar-radiation, ecology, and
  habitat-modelling ops.
theme: terrain
consumed_by: []
produced_by:
  - terrain_aspect
demos: []
status: documented
example_recipes:
  - title: "Aspect from Copernicus DEM 30m via GDAL"
    tool: gdal
    requires: [elevation]
    fixture: copernicus-dem-glo30-iberia-100km
    command: |
      gdaldem aspect -compute_edges dem.tif aspect.tif
    docs_url: https://gdal.org/programs/gdaldem.html#aspect
  - title: "Aspect via Earth Engine ee.Terrain.aspect"
    tool: gee
    requires: [elevation]
    fixture: copernicus-dem-glo30-iberia-100km
    snippet: |
      var dem = ee.Image('COPERNICUS/DEM/GLO30').select('DEM');
      var aspect = ee.Terrain.aspect(dem);
    docs_url: https://developers.google.com/earth-engine/apidocs/ee-terrain-aspect
sources:
  - https://gdal.org/programs/gdaldem.html#aspect
  - Horn, B.K.P. 1981, Proceedings of the IEEE 69, 14-47