1

I am using ArcGIS Desktop 10.1.

My study area is quite large (sometimes spanning across a few grid squares) and when I am running a viewshed analysis or calculating slope or euclidean distance it calculates for the entire region. But at times I just want to concentrate on a very small area (e.g. within a 10 km radius).

In these cases is there anyway to make sure that these analyses just focus on the required area rather than the entire region?

When it calculates for a really large area I am having difficulties with symbology - I can't classify results into anything meaningful!

2

I'm not as advanced as many of the users in this community, but I would clip each area I am interested in and conduct the analysis on each clipped area individually. If you want to keep everything in one .mxd file, you may want to create a Map Book using Data Driven Pages. It's a very efficient way to work on projects with multiple, distinct study areas. Lastly, if this is a long-term project, you may want to look at building a model. You can view a getting started video HERE. I find ModelBuiler provides a great way to organise and improve your workflows. It also partially automates your workflow.

  • it helped immensely! thank you very much! but a quick question, I was looking at some of the videos online about the clipping tool, they usually use a shapefile to define the boundary they want want to clip, is there a way to manually select the area you want to clip? – user19622 Dec 1 '13 at 15:51
  • I mean rather than selecting an area by attributes? – user19622 Dec 1 '13 at 15:59
  • Yes .... there are selection tools. Here's a link: help.arcgis.com/en%20/arcgisdesktop/10.0/help/index.html#//… – Dano Dec 2 '13 at 10:57
  • and glad I could help. – Dano Dec 2 '13 at 11:31
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There are a couple options, actually.

  1. Use Clip to trim the raster of interest (e.g. DEM) to only the area that you want to analyze.

    • Advantage: you have a permanent feature that you can always use -- good for repeated analyses over the same area.
    • Disadvantage: duplicate rasters consume file space and/or can get confusing.
  2. Set the appropriate Geoprocessing Environment (in this case, Processing Extent) so the analysis only operates on a "window" subset of your full raster (or features) of interest. You can set it to the display extents (what your window currently shows), to be the same as another feature (e.g. "match my buffer10km polygon"), or numerical extents of your own choosing.

    • Advantages: no need to create new rasters each time, and the processing environments can be set either globally (through the menu) or each time you run a tool (button on the bottom of any tool's dialog box).
    • Disadvantage: the extent isn't permanently stored (unless you're referring to another existing feature), and, personally, I occasionally forget to reset my processing extent.

Either one will work, although I tend to prefer using the geoprocessing environment to cut down on the number of rasters that I need to keep track of -- just one DEM used for everything, instead of making DEM_full and DEM_10km and DEM_county etc.

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