I am trying to understand viewshed analysis in ArcGIS 10.1.

After you add fields such as RADIUS1, AZIMUTH1 to your observer vector attribute table, does it automatically calculate visible/non-visible areas within the specified radius and azimuth? Or do you have to use a different tool?

What I really need to find out is the areas visible from each monument location (including whether the monuments themselves are visible to each other, if they are close), in such a case what would be the best way to approach this?

Also, is it necessary to always convert xy coordinates of sites (already added as File Geodatabase Feature Class) to Observer points using observer points tool? I am only asking because for some areas, I have more than 16 monuments and I think you can only have a max of 16 observation points.

  • 2
    Have you reviewed the help about Using Viewshed and Observer Points for visibility analysis?
    – PolyGeo
    Commented Nov 25, 2013 at 8:53
  • I get confused about where to actually input values, for instance as suggested below I now know that i need to add the radius, azimuth to the attribute table, but what stumps me is 'then what' - how to get these pieces of information to display the results.
    – user19622
    Commented Nov 25, 2013 at 14:20
  • I recommend that you use the edit button beneath your Question to revise it with these additional details.
    – PolyGeo
    Commented Nov 25, 2013 at 21:32

1 Answer 1


Set up your observer vector attribute table to contain the additional fields (RADIUS1, AZIMUTH1 etc). I haven't used viewshed in Arc for a while as I do it in other ways now but something at the back of my mind makes me think the field names might be case-sensitive (that might have been for the old ArcInfo 7.x on Unix though and might not apply to modern ArcGIS 10.x on Windows). In any event, I always used to name the fields exactly as per the documentation.

If you are testing the visibility of an object in the landscape from all locations (i.e. in this case your points represent a target and not the Observer), just be careful to get OFFSETA and OFFSETB round the right way! Other than that, it is very straightforward.

  • Thanks for the quick reply, really appreciate it! I just want to clarify, when you say additional fields do you mean that this information should be added to the Access Database that has the xy-coordinates? for instance, if I want to see what is visible/not visible with a 10km radius for 15 different sites, do I have a column with 10 written on each row?
    – user19622
    Commented Nov 25, 2013 at 11:05
  • Given that my sites represent observer points?
    – user19622
    Commented Nov 25, 2013 at 11:12
  • You add the RADIUS2 column (or whatever) to your Observer points attributes and in your case have 10000 in each row (assuming your projection units is meters). If your points are observers then there is no confusion - just follow the documentation. Commented Nov 25, 2013 at 12:45

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