topic Re: Polygon reshaping itself issue in Data Management Questions

Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 16:19:26 GMT

I'm having an issue with Arcmap. I have created a new blank shapefile, and am drawing a polygon using the "construction tools" in the editing window. I created the new shapefile, clicked start editing, clicked polygon, and then when I draw the shape I want (I am tracing another layer underneath), the polygon distorts and kind of averages out a few of the areas when I click "finish sketch." I want the polygon to follow the shape I draw exactly, and not cut off extremities. I am not very experienced so I am probably making a simple mistake, any help is appreciated, thanks.

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 16:22:52 GMT

Are you using the trace tool on your edit bar? If not, try using that. Just select the polygon you would like to trace and then start digitizing your new polygon.

Re: Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 16:31:11 GMT

Are you using the trace tool on your edit bar? If not, try using that. Just select the polygon you would like to trace and then start digitizing your new polygon.

Hmm, the image I am trying to trace underneath is not a polygon itself, it is an aerial photograph. Imagine the shape of a building, I want to create a polygon in that shape. However when I trace it out correctly, and click finish sketch, the polygon distorts, cutting offany extremities.

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 16:46:25 GMT

Did you by chance Georeference your image before you started editing?

Re: Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 16:53:54 GMT

Did you by chance Georeference your image before you started editing?

Yes I did, I am georeferencing an aerial photo to a road network shapefile, and then I want to do this tracing so I will have a shapefile of a building boundary.

This is my first time doing this, I created a bunch of control points and got everything lined up correctly. I'm feeling like this is a projection issue based on your response?

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 16:54:59 GMT

This is what I found, read over the answer, that should help you.

Re: Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 17:21:20 GMT

This is what I found, read over the answer, that should help you.

This seems to be the same problem (Phrased much better than mine, of course). When the answer says "The referencing tool was stillopen" and "the georeference wasn't correct," what exactly does this mean? I'm having a hard time understanding what effect the georeference has on the polygon I'm drawing above it, as it is an entirely separate layer.

My steps so far have been.
1. load in road map data, which has a projection
2. load in my aerial photograph (no projection)
3. Line then up as good as possible
4. Use the georeference tool to create control points, which altered the road map and shifted it around to fit inside the streets on my aerial photo.
5. trying to draw the polygon
...

I can see as I click now where it is ignoring my vertices, ie. I click around, and the shape skips over certain ones, but when I click undo vertices to go back I can see that they are definitely there, just being ignored. I feel like I'm missing some fundamental thing ie. I don't understand how georeferencing works that is making everything incorrect. Perhaps I'll just keep reading and watch some tutorials. I appreciate the help very much.

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 17:28:21 GMT

Did you close the georeferencing tool before you started editing? I think that is were the issue is.

Re: Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 17:34:47 GMT

How can I close the tool beyond removing it from the toolbar?

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 17:42:40 GMT

Maybe try and start fresh. Open a new mxd and do steps 1 to 4, at the end of step 4 click on the Georeferencing dropdown and choose "Update Georeferencing". Then remove the Georeferencing from your toolbar, save the mxd and close the mxd. Then re-open it and start editing. Maybe that works.

Re: Polygon reshaping itself issue

dl — Tue, 17 Sep 2013 18:05:57 GMT

Okay, an analyst helped me and here was the solution: I was working in a geographic coordinate system which spanned too large an area for the high level of detail I was working at. We re-projected into an NAD coordinate system close to my area and it works fine now. Thanks for the help, much appreciated.

Re: Polygon reshaping itself issue

TimWitt — Tue, 17 Sep 2013 18:07:42 GMT

Awesome, don't forget to mark the answer, so other people can find it quickly!