topic Re: Creating & selection using density in Data Management Questions

Creating & selection using density

KrupaliVijaykar — Mon, 07 May 2012 06:27:35 GMT

Hello,
I am trying to work on a project where I need to find population data.

One layer has population data of villages (polygon layer of villages, with population in attribute table)
Another layer has a threath zone for a particular disaster (again a polygon layer)

I have to find the population data of villages, which comes under the threat zone only.. (ie. if a particular threat zone covers part of a village, only part of the population data should be the output & not the entire population)

Any suggestions, how I can select only part of population & not just display population of the entire village

Re: Creating & selection using density

HardolphWasteneys — Mon, 07 May 2012 07:42:06 GMT

kvijaykar,

If you cut the village polygons with the edge of the threat polygon and use a numeric domain for your population number field with a Split Policy called Geometry Ratio, the resultant polygons will have population numbers proportional to the areas of the splits. This can also be accomplished by preserving the original village polygon area in a field and calculating the proportions of the new area to apply to the population, which would be useful if you are stuck with shapefiles.

You can see the details of the cutting polygon and geometry ratio process in my recent post in http://forums.arcgis.com/threads/56094-Trying-to-divide-a-large-amount-of-polygons-with-a-single-line-shapefile

You could also employ Analysis Tools > Overlay Intersect with a polygon output between the Threat and Village polygons to select villages and cut villages within the threat zone.

To get an ouline polyline from the Threat zone there are numerous ways including a couple of simple scripts in ArcGIS 9.3 Samples > Data Management > Write Features To Text File and the companion reverse Create Features From Text File . Just input the polygon feature class into the first script, edit the header in the output text file changing polygon to polyline, save and run the second script to generate the polyline.

hope that works for you.

Hardolph

Re: Creating & selection using density

KrupaliVijaykar — Mon, 07 May 2012 09:00:56 GMT

Thank You sir,

Ill certainly try out your method.

One more query, i need to just find the population data (ie. only selection & display of selected population is required). Can this be done in any other way except splitting/ cutting polygon.
This is because ill have to carry out the procedure (of cutting polygon of village layers) on about 3000 threat zone (my project involves a large amount of data).

Re: Creating & selection using density

HardolphWasteneys — Mon, 07 May 2012 17:48:13 GMT

Krupali,

The "Cut Polygon" method can be completed on your entire dataset in one operation in a few minutes. The key is to make a Merged copy of the cutting Lines generated from your Threat Zones polygon Feature Class (or shapefile) via the 2 scripts (http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_the_sample_Features_toolset ) and to use that on your Target Feature Class of Villages. It is the part of the procedure I laid out in the other post (parts 3 to 11) and pasted in below. You should also do the operation on a copy of your Villages FC to preserve the original. The entire operation should not involve any repetitive action and I would not expect it to take very long. The first stage is to set things up in ArcCatalog: 1. create a file geodatabase, 2. import the polygon files, 3. set up a numeric domain ( http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?TopicName=An_overview_of_attribute_domains ) with the Geometric Ratio split policy and apply that to the population field in the villages FC, 4. create a scratch polyline FC and run the 2 scripts with a quick text editor session in between and start up ArcMap....

3. set up a scratch polyline file in ArcCatalog and bring into your map.
4. Start an EDITOR session with Task: Create New Features and Target: the scratch FC. select all the polylines that you want to use as splitters, whether from one shapefile or Feature Class or many (can be in different workspaces too)
6. with the edit tool on the map Right-Click COPY and Right-Click PASTE (makes a safe copy of the lines geometry in your scratch polyline FC)
7. leave the lines selected and hit EDITOR >> Merge and choose any feature as the merge to feature for symbology (it does not matter)
8. Change to TASK: CUT POLYGON FEATURES and Target: the new POLYGON FC.
9. Select the polygons to be split either in the attribute table or on screen (this will activate the SKETCH tool (pencil) in the EDITOR toolbar)
10. select the SKETCH tool and hover over any part of the Merged Polylines (to be sure I set snapping on the polyline FC and MapTips will show when it is being hovered over or snapped to)
11. Right-click and hit REPLACE SKETCH and then F-2 or Right-Click and Finish Sketch.

As I mentioned you can also do this with just shapefiles if you are unfamiliar with domains, but geodatabases do offer more functionality and keep things neater.

Let me know if you run into any difficulties.

Hardolph