topic Re: Problem with raster to vector polygon conversion in Data Management Questions

Problem with raster to vector polygon conversion

EricBrossman — Tue, 06 Aug 2013 16:14:15 GMT

Okay, so I'm feeling lost and overwhelmed so I'll apologize in advance if my questions are a little long winded. I am doing a study tracking the dispersal and habitat selection of captive reared Barn Owls. I'm layering their positions and flight paths over Landsat images from the 2006 National Landcover Database (NLCD).

I found the image on the ArcGIS online, plotted the positions and buffered the flight paths using the buffering tool(I'm using version 10.0). I need to find the percent coverage of each habitat utilized and available to the owls along their buffered flight paths. In order to do this I need to clip the buffered flight paths from the basemap.

Here's the problem: For some reason I cannot clip the paths from 2006 NLCD or attribute the habitats encountered by the owls in their flight paths. The GIS analyst I am working with noted that the map from ArcGIS online was in raster format and in order to attribute the data, it needs to be in vector format. I'm not sure I know what I am doing or what to do. Has anyone else had this problem?

Re: Problem with raster to vector polygon conversion

JimCousins — Wed, 07 Aug 2013 13:23:59 GMT

Rather than clip the data, what about using zonal statistics? This performs analysis within polygon zones on raster data... Assuming you have access to Spatial Analyst extention.
-Jim

Re: Problem with raster to vector polygon conversion

EricBrossman — Wed, 07 Aug 2013 18:05:27 GMT

Rather than clip the data, what about using zonal statistics? This performs analysis within polygon zones on raster data... Assuming you have access to Spatial Analyst extention.
-Jim

I do have access to the extension. Will that work within the buffer zone without clipping from the basemap? I need to get the percent coverage of each habitat type covered within the buffer zones. I've never used the zonal statistics tool before but I'll give it a shot. Thanks

Re: Problem with raster to vector polygon conversion

EricRice — Wed, 07 Aug 2013 20:31:18 GMT

Eric,

Zonal Stats is not going to give you the distribution of the values. It won't tell you the count of every value it finds in the zone - it just gives stats. For your request, you should look into Zonal Geometry as Table or Zonal Histogram. I have a GPK in a thread below to convert the raw count distributions into percentages using Zonal Geometry as Table and some other tools I strung together.

Calculating the area and the percent of cells of each value in a raster (GPK)
extracting information from a Raster landuse file by a polygon shape file
ArcMap - Land use type as a percentage of total area

To use the GPK properly you clip the input raster to the zone (buffer), since the tool has no parameter for zones (polygon zones in addition to the value raster) despite its name. It's referring to the internal zones (values) inherent in the data. In other words, use the value field (or the landcover field). I haven't looked at the service, sorry. Also, the NLCD service you refer to has a max request size limit imposed. Assuming your buffers aren't so large as to exceed the max request size you can clip the service to your buffer and take the result to my GPK.

Or just give Zonal Histogram a go, but it won't give you percentages - just the raw distribution.

Best,
Eric

[h=2]

Re: Problem with raster to vector polygon conversion

EricRice — Wed, 07 Aug 2013 20:53:40 GMT

Here's the problem: For some reason I cannot clip the paths from 2006 NLCD or attribute the habitats encountered by the owls in their flight paths. The GIS analyst I am working with noted that the map from ArcGIS online was in raster format and in order to attribute the data, it needs to be in vector format. I'm not sure I know what I am doing or what to do. Has anyone else had this problem?

Re-read your post. You probably can't clip because the flight path buffer is larger than the max request size on the service. Try it with a polygon known to be smaller than the limit first. The layer is restricted to a 24,000 x 24,000 pixel limit, which represents an area of nearly 450 miles.

For the record, raster data can have attribute tables. See Raster dataset attribute tables for more information.

Best,
Eric