Reinaldo,
The suggestion made by "maptitude-owner" (is that you, Stewart?) will work great so long as you don't have any parcels that are themselves non-contiguous. Ideally, that shouldn't happen, yet I have encountered such parcels in a shapefile provided by our local county. I came up with an alternative solution, inspired by a game called "monster tag" that kids in the U.S. sometimes play. In regular tag, the kids take turns being "it" (you tag someone and run away). In monster tag, each child who gets tagged is added to the group of kids who are "it" until there's only one kid left (Do they play that in Brazil?). You pick a polygon, select all of its adjoining polygons, then all of the polygons adjoining the group (and so on and so on) until all of the contiguous polygons have been found (the game is over). Then you pick another polygon that wasn't part of a game yet, and start a new game... and so on, and so on, until all polygons are exhausted. What's the difference? Imagine you applied the area-lines-area hack to a file with just 2 U.S. states: Michigan and Wisconsin. The state of Michigan would get split into two parts: The upper peninsula would be in one district with Wisconsin, while the "mitten" would stand alone as a separate district. My solution would treat Michigan as a unit, putting the entire territory of the two states in a single district. Either solution has its merits, depending on how you would want to treat non-contiguous parcels. I would also imagine that one solution would run faster than the other (though I have no idea which). Anyhow, I've posted my solution to Directions Magazine (http://www.directionsmag.com/files/view/cluster-contiguous-0.2/166139) in case folks find it useful. GPL v3 license, and all that. --- In [email protected], [email protected] wrote: > > Hi: > > You could create a formula field with a single value, e.g. 1. > Use Merge by Value to merge all areas into a single polygon. > Use Tools-Geographic Utilities-Line/Area Conversion to convert the > merged areas into lines. > Use Tools-Geographic Utilities-Line/Area Conversion to convert the lines > back into areas. > > Maptitude Mapping Software <http://www.caliper.com> Group Moderator > > > --- In [email protected], Reinaldo Paul Pérez Machado > <rpmgis@> wrote: > > > > /*Hi guys, > > > > I would very much appreciate your advice here. I have to perform a > merge > > by value operation over a polygon geographic database with more than > > 300000 parcel records. In the first attached image > > (MergeByValueProblem1.png), I have place a small sample to show what > is > > all about. As you can see, every single polygon is an individual area > > with full topology and corresponding ID. I have to merge all clustered > > or contiguous polygons (sharing at least one border) into a new one, > > that is dissolving the internal lines to produce a bigger resulting > > area. I would normally use the Merge by Value command, but the problem > > here is that only the clustered polygons should be merged and the > > resulting polygons should have a individual new ID (just in case that > > some merging was produced), area and perimeter, and all previously > > isolated areas should remain like that. In the above described example > > the successful operation should ends up with just 7 polygons (see the > > other annexed sample, MergeByValueProblem2.png). > > > > As I have said the real set is simply too big to do this by hand, so I > > would have to find some kind of automation on the process. As an > > additional information there are regions (see the black thick line) > that > > encloses subsets of this small parcels so it is possible to perform > an > > attribute tagging in order to identify which parcels belong to each > > region or "districts" but again the resulting standard merge by value > > operation would result on a non desired result. > > > > Thanks in advance for any aid you could provide on this matter. > Cheers, > > > > Reinaldo*/ > > > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Maptitude/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/Maptitude/join (Yahoo! ID required) <*> To change settings via email: [email protected] [email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
