topic Re: Generating Elevation Polygons from Contour Lines in Data Management Questions

Generating Elevation Polygons from Contour Lines

ElizabethB — Wed, 26 Sep 2012 14:54:45 GMT

Hello All-
I am running ArcGIS 10.1 (just recently upgraded). I am working on a project to create polygons of elevation. Currently all I have to work with are 2 meter contour lines for my county. Is it possible to create polygons from this polyline layer? Should I try to obtain LIDAR data instead? (someone told me that LIDAR would create polygons?) Will I need an extension like Spatial Analyst to accomplish this? Since these are contour lines very few of them actually intersect (except the rings) so when I try to use the Construct Polygons tool it only did a few of them. I need to figure out a way to close these lines, I suppose.

Has anyone done this type of project before, or can recommend a starting point? Thanks in advance!

Elizabeth Brumfield
GIS Specialist
Santa Rosa County Property Appraiser's Office

email: ebrumfield@srcpa.org

Re: Generating Elevation Polygons from Contour Lines

michaelcollins1 — Wed, 26 Sep 2012 15:31:17 GMT

The question is "Why do you need to?".

If you do, you'll need Spatial Analyst or 3D Analyst.

I suppose you could convert the polylines to points and then interpolate a surface using Spatial, or create a TIN from the contour lines using 3D.

Re: Generating Elevation Polygons from Contour Lines

ElizabethB — Wed, 26 Sep 2012 15:45:20 GMT

The question is "Why do you need to?".

If you do, you'll need Spatial Analyst or 3D Analyst.

I suppose you could convert the polylines to points and then interpolate a surface using Spatial, or create a TIN from the contour lines using 3D.

My boss wants to eventually overlay the new polygon layer with parcels to show...I believe...elevation values that could be important in storm surges (we are a coastal county). He does NOT want to use a storm surge layer, he just wants to be able to see elevation in relation to parcels, mostly along the coastline. And honestly, he might just be seeing what I can do w/this project (it's my 2nd week on the job!)

I was hoping to avoid having to request the purchase of an extension to complete this project. Can I just create a bounding polygon and then try to construct polygons from the lines? Is this strictly a Spatial Analyst task?

Thanks!

Re: Generating Elevation Polygons from Contour Lines

HardolphWasteneys — Wed, 03 Oct 2012 05:56:05 GMT

Elizabeth,

A bounding polyline that intersects the open contours will probably do the job. However, you may find that some contour lines are discontinuous and need to be connected or merged. You do not need Spatial Analyst or any extensions, just the basic ArcView or whatever it is called in 10.1 unless you would like to make a raster image using the contours, which requires Spatial Analyst.

I'm not familiar with the 10.1 Construct Polygons tool, but it probably works along the same lines as the procedures that work in ArcView 9.x and 10 using "Auto-Complete Polygon" described in some of my other posts including some involving contour maps with links below.

http://forums.arcgis.com/threads/6786-polyline-to-polygon?highlight=Hardolph
http://forums.arcgis.com/threads/5189-how-to-create-polygons-from-digitized-contour-polylines?highlight=Hardolph

In all cases you need closed polylines and I recommend copying all the lines of interest to a "scratch" file where you merge them as the basis for forming the polygons. The lines can be copied from many different layers so your bounding polygon can be a separate feature class/shapefile.

Hardolph

Re: Generating Elevation Polygons from Contour Lines

ElizabethB — Wed, 03 Oct 2012 13:57:28 GMT

Elizabeth,

A bounding polyline that intersects the open contours will probably do the job. However, you may find that some contour lines are discontinuous and need to be connected or merged. You do not need Spatial Analyst or any extensions, just the basic ArcView or whatever it is called in 10.1 unless you would like to make a raster image using the contours, which requires Spatial Analyst.

I'm not familiar with the 10.1 Construct Polygons tool, but it probably works along the same lines as the procedures that work in ArcView 9.x and 10 using "Auto-Complete Polygon" described in some of my other posts including some involving contour maps with links below.

http://forums.arcgis.com/threads/6786-polyline-to-polygon?highlight=Hardolph
http://forums.arcgis.com/threads/5189-how-to-create-polygons-from-digitized-contour-polylines?highlight=Hardolph

In all cases you need closed polylines and I recommend copying all the lines of interest to a "scratch" file where you merge them as the basis for forming the polygons. The lines can be copied from many different layers so your bounding polygon can be a separate feature class/shapefile.

Hardolph

Thanks very much for this! Will give it a go, and thanks for the input on Spatial Analyst. We are too close to the end of our Fiscal Year to purchase extensions.