Amanda Hargis

Using Regions to Organize Overlapping Land Use Planning Areas

Abstract:

Defining Issue: Ink on paper maps, and standard polygon attribution, can't deal with the overlapping and multiple parcels involved in Subdivision Exemptions.

GIS Solution: REGIONS provided the ability to store and retrieve the overlapping polygons involved in this process. A series of AMLs and menus was developed to aid in the input of the regions, and accessing the final information is done through ArcView.

Methodology: Various AMLs and menus allow a technician to create and attribute overlapping Subdivision Exemption regions out of parcel polygons. This information was added as a theme to an existing County planning ArcView project, so that the planners can click on a parcel to determine if any subdivision exemptions have occurred on that parcel.

Software: The Subdivision Exemption Regions application was written using AML, with menus created in Formedit. Access to the data is accomplished via Avenue scripts.

The purpose of this paper is to discuss methods of getting regions into a database, pitfalls found and overcome, and methods of allowing non-technical users to create and access the new regions.

Boulder County GIS

Boulder County's GIS was started about 10 years ago. The project was started as a way to more easily maintain the 750 section maps defining assessed land for the County Assessor's Office. Each section, quarter- section, or township map was recreated as a single coverage. This group of parcel coverages has become our base layer, which all of our other layers are tied to.

The Subdivision Exemption project

Subdivision Exemptions (SEs) are the result of a process through which the county recognizes changes in parcel boundaries without the full Subdivision approval process. Typically they involve moving an ownership boundary to reconcile a conflict or encroachment or division of land between two already existing uses. The Land Use GIS's goal was to take the existing paper Subdivision Exemption files and create a coherent ArcInfo coverage of the parcels that have gone through the SE process.

Why regions?

In nearly every case a SE involves multiple parcels and/or polygons. Frequently multiple SE approvals involve the same parcels. They are certainly the type of situation for which the region feature type provides the appropriate description.

Setup of project

The existing Subdivision Exemption information consisted of hand-drawn outlines on a 1:50000 map, six file drawers full of SE application file folders, and a box of microfiched applications.

Boulder County's base layer consists of parcel information, so the easiest thing to do to create a new layer is to start Arcedit, grab the arcs that define the polygons we want, and PUT them into a new coverage. We had an existing application written using AMLs and menus to facilitate grabbing arcs, and so rewrote that to make the areas into Regions.

The user is given the section, township, and range in the SE file folder, and sets that section as her mapextent with a "Zoom In" button on a menu in Arcedit. The section is drawn as a backcoverage while existing regions and polygons are colored on the screen in the SE coverage that is being added to. Without changing the appearance of the coverages on the screen, the editcoverage is changed to the base parcel coverage, the user selects the appropriate arcs that define the parcels involved in the SE, and then those arcs are PUT into the SE coverage.

At this point, the coverages is unclean, and no topology exists, because arcs were introduced to it. In order to create a region, the user must save the coverage and clean it, and then select polygons to make into a region. The user has a choice at this point to continue selecting arcs from different parcel coverages, or to clean the SE coverage and create a region. If any on-screen editing needs to be done, the user can choose editing options from a menu.

Once the SE coverage is cleaned, the user selects all the polygons necessary to define a particular SE, and fills in attribute information in a form menu. Attributes we keep track of are Applicant's name, Subdivision Exemption file number, which is separated into year and number (for example, SE-95-03 would be Subdivision Exemption 03 in 1995) and whether the application was approved, denied, or withdrawn. All other information about the SE is stored in a separate docket tracking application.

Problems in project

Despite reading everything I could on Regions, I still didn't have that "oh yeah!" understanding of it at first. I went through all the motions, and created files, and didn't really understand what was going on. That took a while. Once the lightbulb lit up over my head, the project went a lot more smoothly.

The biggest problem was the fact that, when dealing with regions, you can be in editfeature poly, editfeature arc, or editfeature region.subclass. If you add or delete polygons or arcs to the region, and then try to clean the coverage, you end up with an error message "unclosed ring in region #". This was very frustrating. The online docs revealed no clues to the solution, and tech support, when emailed, merely suggested reading the online docs.

One other problem we have faced is that the interface we designed allows for the user to select a region and then attribute it. However, when selecting regions, the first region created is automatically selected first, which can create confusion if the region boundaries are coincident.

Solutions to problems

Trial and error, experimentation and failure, were the ways we came up with our solutions. We have learned to use only editfeature region.subclass when dealing with already existing regions. We have learned to adapt our existing arc and polygon based AMLs and menus to deal with regions, and to be flexible.

All in all, using regions has proved to be the best way to solve our need to attribute and retrieve information on overlapping polygons.

Where do we go from here?

We are still in the process of creating and attributing regions, as of the writing of this paper. By July, we will probably be finished with that step of the process, and begin creating an interface for the Land Use Planners to access the data that we have created. Most likely, that interface will be in ArcView 3.0, rather than in ArcInfo.

Did regions work for us?

Using regions was definitely the best solution for the spatial problem we had. Since starting this project, we have defined other projects that will be perfect for a regions application. We are excited to be using this method of storing and retrieving overlapping spatial information.

Will we use regions again?

We are planning on using regions to keep track of areas that the different municipalities in the County have proposed for annexation; if they have been annexed; how many potential housing or commercial units each area has; how much of the potential has been built, and other such Land Use planning statistics. We have found regions to be very useful in keeping track of overlapping planning areas.

Amanda Hargis
Senior GIS Specialist
Boulder County Land Use Dept.
P.O. Box 471
Boulder CO
80306-0471
voice: 303.441.3930
fax: 303.441.4856
email: aemlu@boco.co.gov

Many thanks to Ken Ziebarth, kezlu@boco.co.gov and Carmen LeRoux, cdllu@boco.co.gov for their assistance and hard work on this project.