Raster Functions

A raster is a geographic dataset that consists of pixels which are organized in rows and columns. Each pixel has a value, such as elevation. Each pixel also has an x and y coordinate which gives it a location.

A raster function is a defined processing operation that can be applied to a raster. The on-the-fly application does not change the underlying raster data, just how it is displayed. On CT ECO, raster functions are available for image services of DEMs (digital elevation models, or pixel based bare earth elevation).

Elevation Services on CT ECO with Raster Functions

They are evident by the year at the end. The aspect, elevation, hillshade, shaded relief and slope are based on the 2016 DEMs and already have a function applied.

Statewide 2016 More info REST
Central 2014 More info REST
Coast 2012 More info REST
East 2010 More info REST
Northwest 2011 More info REST
Southeast 2011 More info REST
Southwest 2011 More info REST


Apply a Raster Function in ArcMap

Once Arcmap is open,

  • First connect to an elevation service that has functions available. Help here if you need it.
  • Once the elevation service is in ArcMap, open Layer Properties (right click and choose Properties or double-click on the name).
  • Locate the Processing Templates tab and the functions available. Select a function and click Apply.


Apply a Raster Function in ArcGIS Online

Go to arcgis.com, log in and add an elevation service from CT ECO. Detailed instructions here if you need them. Remember to add one of the services that has functions.

  • Click the three blue dots to open the menu then choose Image Display.
  • Choose the renderer, or function from the dropdown list. Optionally, choose a stretch. Click Apply. The elevation is now shown with the function applied. Note that the same service can be added multiple times with different renderers applied.


Raster Functions

Aspect can be thought of as slope direction. The values of the aspect layer are the compass direction of the slope with north being 0, east being 90, south being 180 and west being 270.

Hillshade is a grayscale model of terrain with the sun's angle taken into account for shading the terrain.

Shaded Relief is a color representation of the terrain that takes the sun's angle into account.

Slope represents the rate of change of elevation. The output is shown in degrees from 0 to 90.