7 replies to this topic

[ELeFevre]

I am trying to dissolve all of the states within the U.S., so all that remains is the outline of the U.S. In the past (9.1) I thought I was given the option to dissolve on the shape field, but now I'm not seeing the shape field listed as an available field to use (I upgraded to 9.2 earilier today). Of course I can dissolve using other fields but the output contains a few stray artifacts. It would great to get a clean boundary in one swoop. I've done this countless times in the past with great results, and I sware I used the shape field. Maybe I've finally lost my mind.

[Charlie Frye]

Erin,

It's been a while since I last did dissolve that way (summarize by shape was how I remember it); the current dissolve tool never worked that way.

There are two other ways to do this, one is to add a short integer field and calculate its value to 1 and dissolve on that field. The other is to copy the data and then start editing the copy, select all the features and then from the Editor menu choose Merge. If you're unsure of the topology (and want to avoid sliver polygons), then run the Eliminate tool (or build a topology and manually fix the errors if you need to ensure the correct elimination is made).

Charlie

[Martin Gamache]

I thought you could run dissolve without choosing a field and it was the equivalent, it just dissolves everything together.

But it seems there has to be a better way to get an outline of the US no....doesnt one already exist?

mg

[CHART]

Erin,

If you have MapInfo. Just need to select your states and do a Combine.... (a bit like Martin suggests can be done with ArcGIS).

I am not anti-ESRI (still using my old ArcCad for topology and ArcView 3.3) but sometimes it seems you need to do a lot of flips to achieve what seems at first like a simple task.

[ELeFevre]

Charlie,
Thanks for the reply. I tried the first method you suggested and it worked great. Thanks. There were a few sliver polygons remaining but they were easy to remove. I haven?t gotten around to your second suggestion. I?ll give it a shot when I get a minute.


Martin,
Thanks as well. Yes, running the dissolve without any fields selected worked. I assumed that a field was necessary to do this. Also, I was just using the US as an example. I use boundary files on most maps (I apply gaussian blurs and outer glows to these) I wanted to know how (or try and remember) how to create my own for other parts of the world.

Jacques,
Thanks for your input. I have a copy of MapInfo on my machine but I rarely use it. I?m a fairly dedicated Arcview user these days. However, I?ll give your suggestion a try.

On a slightly different note, I think could do the same thing (create a nice boundary) by selecting a shape, e.g. the US in Illustrator and then combining those paths.

[mattm]

To complete the dissolve in Illustrator just select all the artwork ex. states, then in the pathfinder palette click the "add area to shape" button (the furthest left button under shape modes), then click the expand button. This will dissolve the boundries for the entire area.

[Charlie Frye]

I thought you could run dissolve without choosing a field and it was the equivalent, it just dissolves everything together.

But it seems there has to be a better way to get an outline of the US no....doesnt one already exist?

mg

In spirit, I agree with Martin; most of our work though, in the last few years has been pretty geared to supporting automation. An aspect of this is also to provide the most flexible tools within that environment, and that flexibility can sometimes translate into extra baby steps within scripts and models.

Also, a third way to do this is to create a new line feature class, add it and your state polygons to a new map, start editing, select the polygons, and then use the trace edit sketch tool to create an outline.

And a fourth way... Use the polygon to line tool (versus the feature to line tool)-- you will get a set of linework that is broken at all the intersections, allowing you to select tag an attribute of the lines as either interior or exterior. The exterior can then be broken by intersecting with lakes, or manually to tag them as being coastlines or interior political boundaries.

[BZero]

Speaking of dissolving. What is the best way to dissolve a shapefile with say over 1 million record without getting a memory limitation error? All in all in order to reduce file size.

Is it just a matter of selecting maybe 1/4 of the files and dissolving 250,000 records at a time, and then rejoining the 4 files when you are done?