Topic: topology and islands

[gisdude]

Hi all,

I am wondering if anyone has experience(or a technique) for making a map topology with "islands"? I want to build a topology of a Specific Plan that we are starting to work on and I have a couple of Open Space polygons that have a pedestrian  walkway that "cuts" through.

I have built many topology's but this is a new one to me. I can do it in ARCVIEW, but Autocad Map has a problem with making the "ped" crossing it's own polygon.

I read on one of the posts that mpolygons are supposed to handle this, problem is you can't export to .shp files with mpoly's.

Also, is it better to create a topology with polylines or just lines? I didn't know that there would be a difference when you choose between the two.

Thx a lot,

[sinc]

Hi all,

I am wondering if anyone has experience(or a technique) for making a map topology with "islands"? I want to build a topology of a Specific Plan that we are starting to work on and I have a couple of Open Space polygons that have a pedestrian  walkway that "cuts" through.

I have built many topology's but this is a new one to me. I can do it in ARCVIEW, but Autocad Map has a problem with making the "ped" crossing it's own polygon.

AFAIK, there is no way to create overlapping areas in a topology, or an area that is included in two different polygons.  You should be able to create a "walkway" polygon, but then the "Open Space" polygon would be the polygon(s) surrounding it.

I read on one of the posts that mpolygons are supposed to handle this, problem is you can't export to .shp files with mpoly's.

Sorry, can't help you with this.  I don't use .shp files for anything except custom linetypes, so I can't help you with a conversion.  But Map Topologies are supposed to be easy to export to other GIS applications...

Also, is it better to create a topology with polylines or just lines? I didn't know that there would be a difference when you choose between the two.

I don't really understand this...  You are running Drawing Cleanup before you create your topology, right?  When you run "Drawing Cleanup", it should fix everything so that you have the proper "links" for creating your polygon topology.  It doesn't matter how you draw your linework, just make sure you run it through Drawing Cleanup with the proper options (break crossing objects, etc.).  A link can be either a polyline, a line, or an arc, but it must be a solid link.  Drawing Cleanup (with proper settings) should take care of everything for you, and convert all your linework to solid links, no matter how you draw them.

As far as getting proper settings into Drawing Cleanup, that can take some trial and error...

[LE]

...  You are running Drawing Cleanup before you create your topology, right?  When you run "Drawing Cleanup", it should fix everything so that you have the proper "links" for creating your polygon topology.  It doesn't matter how you draw your linework, just make sure you run it through Drawing Cleanup with the proper options (break crossing objects, etc.).  A link can be either a polyline, a line, or an arc, but it must be a solid link.  Drawing Cleanup (with proper settings) should take care of everything for you, and convert all your linework to solid links, no matter how you draw them.

As far as getting proper settings into Drawing Cleanup, that can take some trial and error...

I am just curios, about what it is "making a topology & dwg cleanup"... do you have a drawing sample I can have a look if it is possible? or a link to where I can find that info? thanks.

[Jeff_M]

Luis, these are AutoDesk Map3D terms. See THIS for a link to the Autodesk Map 3D 2007 User’s Guide (pdf - 11771 Kb) and other things. The user guide should describe these well for you.

[gisdude]

sinc,

I AM doing drawing cleanup. That is not a problem. The problem comes up when I want a topology AFTER doing the drawing cleanup.

As I said before, my Open Space has to be 1 POLYGON. I have to take into account the acreage of the pedestrian walkway, that will prolly be at least .5 acres if not .6. This must be docutmented in the application to the city.

When I get to work tomorrow I can upload a screenshot of what I'm trying to do.

Thx,

[sinc]

sinc,

I AM doing drawing cleanup. That is not a problem. The problem comes up when I want a topology AFTER doing the drawing cleanup.

As I said before, my Open Space has to be 1 POLYGON. I have to take into account the acreage of the pedestrian walkway, that will prolly be at least .5 acres if not .6. This must be docutmented in the application to the city.

So the walkway is completely inside the Open Space polygon?  AFAIK, you cannot have an area that is part of two polygons at once (overlapping polygons).  So, it sounds like what you want to do is put your walkway on its own layer, and don't select that layer when you build your topology.  You will not have a "Walkway" polygon in your topology, just an "Open Space" polygon.  If you also need to label the area of just the walkway, you'll need to calculate that seperately, either by creating a second topology for just the walkway, or by turning the walkway boundary into a closed polyline, or something like that.

If for some reason you must have a "Walkway" polygon in your overall topology, then there is no way to also have that area be part of your "Open Space" polygon in the same topology.  Instead, you would need to have a "Walkway" polygon and an "Open Space (minus the walkway)" polygon (and maybe more "Open Space" polygons, if the walkway completely splits the open space).  Then you would just have to do manual cleanup on your labels, to make them look the way you want.

[gisdude]

i see says the blind man.

i kinda get where you're leading me to. it seems i can make a "primary" topology when i create it, i just select the Open Space polygon, but be sure NOT to select the Pedestrian walkway.

THEN, i can create a second topology, for the walkway only. This puppy could get pretty complicated. Depending on the number of "islands" and complex polygons.

this is a start...

[sinc]

THEN, i can create a second topology, for the walkway only. This puppy could get pretty complicated. Depending on the number of "islands" and complex polygons.

I'm not sure how complicated a scenario you have...  But is it something where you can create two and only two topologies?  One topology is your main topology.  The other would be for your walkways, and just contains a mix of "Walkway" polygons and "Other" polygons.  Assuming you use layers correctly, with the right Annotation definitions, it might be relatively painless...

You know that you can have islands in a topology, right?  So if you have an area completely enclosed by another area, with no edges touching, you can still use it?  It's just that the surrounding area is a seperate polygon than the island.  For example, imagine a doughnut (two concentric circles).  You can turn that into a topology consisting of two polygons.  But the area of the outer polygon does not include the area of the inner polygon.