0

I'm trying to display a number of sea level scenarios to discuss landscape differences across time. I've created a CTM of the region now I need to display sea level at a number of reduced levels (e.g. -50m).

I've already tried extract by attribute using "value <=-50" which produces a number of error problems which seem to be related to the GDB, but I can't get round them. Could extract by mask be better?

Does anyone have a simpler or better way? In an ideal scenario I would like to display the final model with terrain changes displayed for the terrestrial data but the sea can be extracted as no data and displayed blue. However it can simply be a blue green display just showing coastline if that is the best way using ArcMap 10.3, Windows 8.

  • 1
    Have you tried Raster Calculator? This assumes you have Spatial Analyst – Barbarossa Feb 16 '16 at 13:57
  • @Barbarossa I do have spatial analyst. Could this be used to extract direct to new raster? or to create shapefile to be used as a mask? – SPG Feb 16 '16 at 15:03
  • CTM == "Coastal Terrain Model", correct? Is a CTM different in any way from a raster based DTM (Digital Terrain Model)? Does it include bathymetric data? – Leo Feb 16 '16 at 15:14
  • @LeonB yes it a DTM. It does inc. data from bathymetry but its merged as a continuous dataset so displays as seemless, if that makes sense. The only difference is negative values exist in the elevation column – SPG Feb 16 '16 at 15:19
3

There are many approaches you could use to extract portions of your surface model. With Raster Calculator, you could extract cells based on values. For instance, with the Con() statement you could do something like this:

Con("CTM_Raster" <= -50, 1, 0)

This will generate a new raster with a value of 1 for values less than -50, and 0 for those greater. Of course, you will need to change the name of the raster. This can then be used to create a polygon if desired. And as I said, there are other ways.

EDIT

If you wish to retain the original raster values, you can do the following:

Con("CTM_Raster" <= -50, "CTM_Raster", 0)

This will generate a raster with the original values below -50, and a value of 0 above.

  • I've just tried two techniques, your raster calculator and Raster Reclassify. Both produce good simple outputs. That said is there anyway to extract the data values for the area above -50 (in this example). – SPG Feb 16 '16 at 15:46
  • See my edited answer – Barbarossa Feb 16 '16 at 15:49
  • For anybody looking at this all three solutions mentioned work! @Barbarossa was most useful in this case for future use (i.e. if I need to run anymore spatial work through it). The use of two differently displayed rasters (@LeonB) maybe be the best for publishing. – SPG Feb 16 '16 at 16:16
2

Here is a simple solution by playing with the display. (I think you would need to adjust display settings anyways to get what you're trying to do, regardless of whether you make another raster layer or change a range of cell values, right?)

This example uses the National Elevation Dataset 10m, but I display it twice, once to use the stretched symbology and hillshade for the land, and then overlay that with a layer using classified symbology. The classes are set to elevation values where the break is at the elevation you want to display sea level. Color the class below sea level blue (or your choice), and the above sea level set to "No Color" so that the stretched value, "land" layer shows through.

  1. Display the CTM or DEM/DTM twice:

enter image description here

  1. Use classified symbology for the layer to show the sea level, set break at desired sea level elevation: enter image description here

  2. Example 1: enter image description here

  3. Example 2: (higher sea level) enter image description here

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.