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Merging Polygons- need help on a super easy subject!

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#1
puffpuff1013

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Hi everyone! I know this is a really basic question, but I am really new to GIS and can't seem to figure it out. I am using a United States map from tiger. Each state is broken up by county. I need to merge the counties into larger sections (smaller than states but larger than counties). I know that when using the editor tool bar, I can select the features I want to merge, then click merge under the editor tool bar. My problem is that I can not click "merge" on the editor tool bar (it is in light gray). Am I doing this wrong and also is there an easier way to merge multiple polygons within a state? I know I can do syntax but I am not skilled with that at all! Thanks for any help!!!

I am using ArcMap 9_3

Edited by puffpuff1013, 19 April 2010 - 03:22 PM.


#2
Hans van der Maarel

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It'd be useful if you could tell us what software you're using.
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#3
puffpuff1013

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It'd be useful if you could tell us what software you're using.


Hi, thanks for the response. I am using ArcMap 9_3. Any suggestions?

#4
Matthew Hampton

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It'd be useful if you could tell us what software you're using.


Hi, thanks for the response. I am using ArcMap 9_3. Any suggestions?


I think the geoprocess you are looking for is "Dissolve." You can search for it in your Toolbox. It should work on selected features, but can be used on features that share a common attributes. You might also be interested in checking out the very large user group that is specifically related to ESRI software. It can be found on ESRI's website.

co-cartographic creator of boringmaps.com


#5
puffpuff1013

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It'd be useful if you could tell us what software you're using.


Hi, thanks for the response. I am using ArcMap 9_3. Any suggestions?


I think the geoprocess you are looking for is "Dissolve." You can search for it in your Toolbox. It should work on selected features, but can be used on features that share a common attributes. You might also be interested in checking out the very large user group that is specifically related to ESRI software. It can be found on ESRI's website.



Do you know the link for that user group? I was under the impression that I had to be ESRI staff to post a message there.

#6
James Hines

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Goto the tool bar & find that red toolbox to activate if you don't see Arc Toolbox in the screen. What you are looking for is not the dissolve tool, all that does is create a new coverage that shows a dataset combining features based on a similar attribute. The dissolve tool is very useful for data such as road networks where you get broken up lines that contain road names & you need to merge all lines containing the same road names. There is a drawback that when dissolve a road name containing something like Main Street that where we are talking about Tiger data that there maybe another town containing Main Street so in essence you are combining both streets called Main Street from both towns. MAPublisher knows how to avoid this & is a tool that GIS manufactures should take idea's from because Avenza has an additional attribute to dissolve your features on: where in this case dissolve everything with 'X' amount of pixels. That's another topic altogether.

What you need to do is the Merge Tool where in the Arc Toolbox under Data Management Tools select General then select Merge. What you are going to do is create a single coverage of all the shapefiles that you want combined. Once you see the popup you will see a brief explanation of the Merge tool, now start by clicking the folder in the top form line then scroll over to the folder containing the datasets you want to merge. Select all of the datasets, then scoll down in the Merge Datasets popup to the Output file dialog & change file path if needed & name your coverage. I don't think you need the optional Filed Map so ignore that & let it process. If I'm correct the dataset should automatically appear in ArcMap.

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#7
DaveB

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It'd be useful if you could tell us what software you're using.


Hi, thanks for the response. I am using ArcMap 9_3. Any suggestions?


I think the geoprocess you are looking for is "Dissolve." You can search for it in your Toolbox. It should work on selected features, but can be used on features that share a common attributes. You might also be interested in checking out the very large user group that is specifically related to ESRI software. It can be found on ESRI's website.



Do you know the link for that user group? I was under the impression that I had to be ESRI staff to post a message there.

try ESRI forums
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#8
Matthew Hampton

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The important difference b/w 'merge' and 'dissolve' is that 'merge' will create a new feature that retains individual records, while 'dissolve' will create a new feature that only has one record.

In your case - if you wanted to create a new feature from of several counties, but you needed the counties to retain their boundaries (and distinctive attributes) then use 'merge.' If, however you wanted to create a new feature out of several counties, but you wanted a single polygon (that removes the county boundaries) then use 'dissolve.'

From your description - I felt that you were looking to create new composite shapes that did not retain the respective boundary information. In either case - the ESRI Forums that Dave suggested are a great place to find ESRI specific information.

co-cartographic creator of boringmaps.com


#9
Dolores

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Hello all at CartoTalk,

I’m a fellow budding cartographer from Scotland and I came across this post whilst doing some research for my current thesis and wondering if you could give me some tips in this same issue?

The two issues of merging and dissolving is what I’m having some difficulty in comprehending. Basically part of my thesis is to create a 3 rasters
Which are
1- high constraints
2- Medium constraints
3- Low constraints
4- Positive constraints

So each raster will appear as one large raster so I can then process it in a raster calculator.

So I have 12 data sets which make up the raster’s, and are all now all polygon shape files.

So for the high constraints raster which will have a value of 4 is made up of
6 of the datasets (which are currently 6 separate shape files) and make them into one massive polygon shape file so I can then turn it into a raster, then reclassify it with a value of 4 being a high constraints raster?

So do I a) merge them all together, by making an extra field in all the data sets and like joining them thought that way?

Or B) Do I dissolve them together?

I do not have a lot of experience in either of the tool set so some expert advice would be so very great full.

Thanks for now and really appreciate any advice.

:)

Dolores de Sancha
University of Glasgow
B.Sc. Geography, MSc Geomatics




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