Dr. Stuart B. Murchison, C.P.

Planning and Implementing a Cadastral GIS: Dallas Central Appraisal District

The Dallas Central Appraisal District (DCAD) planned the implementation of a GIS for three years before the first plat map was scanned. A systematic approach of user input, software/hardware evaluation, membership in a local GIS Consortium, recruitment of technical personnel and critical utilization of outside consultant pools has led to a very accurate, relatively inexpensive, and useable system. The combination of different levels of application software and the training of manual drafters as Digital Cartographic Specialists, has allowed the District to transition employees during the implementation stages, while maintaining the system.

Introduction

In 1994, the Dallas Central Appraisal District obtained cost information for three SUN UNIX workstations and three copies of ArcInfo to begin a Pilot Project for the conversion of paper appraisal maps into a dynamic geographic information system. The first task identified by the newly created GIS staff was to evaluate the "end user" needs and requirements. This stage consisted of understanding the primary goals DCAD was formed to complete. How could a GIS assist DCAD in performing their appraisal duties that consisted of mass appraisal of over 670,000 tax parcels? User input, in the form of surveys, needs assessments and evaluation of present appraisal techniques were conducted to determine the most efficient course of action (Larsson, 1991). The Pilot Project began to answer these questions while discovering the amount of labor involved in converting paper maps into digital GIS coverages. Cost estimates arising from the Pilot Project were based on hardware, licenses and staffing to complete the identified tasks to support map conversion within a three-year period. The hardware requirements were met with SUN UNIX workstations and ArcInfo. The Pilot Project identified the number of workstations and personnel required for completion of the implementation stage. These estimates required eight SUN workstations and eight GIS staff specialists, three workstations/staff specialists for appending and annotating maps and five workstation/staff specialists for full digital map maintenance.

In addition, the estimates included hardware which was not anticipated during the Pilot Project but considered essential to overall implementation success. This included a T-1 communications link to the newly formed North Texas GIS Consortium, the 10 Base T network connections, funds for consultants in data base design and customization, a relational data base, training and customer viewing workstations. In early 1996, after the DCAD Board of Directors approved 2.2 million dollars for a three-year GIS implementation phase, the atmosphere of GIS was evolving from the UNIX world to Windows based platforms. DCAD decided to obtain an experienced GIS Manager to evaluate the Implementation Study for cost and feasibility, recommend direction concerning hardware paradigm shifts, review personnel requirements, implement the project and develop training techniques while preparing future customization screens for the appraiser staff.

A. Retroactive Planning and Implementation Strategies

Significant progress had been achieved in the microcomputer industry, which the District thought advantageous. The high cost of the UNIX equipment and its significant maintenance fees where quickly overshadowed by the relatively low cost and inexpensive maintenance contracts offered by personal computers running Windows NT operating systems. Most hardware aspects in the PC environment were less costly, equally powerful and integrated well with legacy hardware already in place at the District. Software advances ran parallel with hardware advances, promising greater utility at reduced costs. Peripheral equipment, such as networks, digitizers, scanners and tape backups were soon joining the industry, as migration to PC's became an overwhelming economic reality.

Forces of change were also occurring as the microcomputer industry boomed. These changes consisted of an increased number of experienced GIS consulting firms, increased awareness and leverage of legacy equipment and availability of pertinent information to ease the decision making process.

1. Hardware Retooling

It was decided to switch from UNIX SUN equipment to Windows NT PC's. An RFP was released and DCAD soon took delivery of a PC Server and three workstations running Windows NT 3.51. The reduced budgetary cost in hardware licenses, maintenance and ancillary software allow the GIS Division to purchase top-of-the-line PC's and distribute them among the Appraisal Divisions for testing. The PC's performed at an acceptable level and were fitted with the existing peripheral hardware. The District has since upgraded the OS to Windows NT 4.0 with increased performance.

2. Consortium Membership

The formation of the North Texas GIS Consortium was a very timely occurrence for DCAD. The consortium, founded by The Bruton Center for Development Studies at the University of Texas at Dallas, was originated as an association of municipalities, appraisal districts, school districts, utilities, and universities committed to sharing information. This consortium is directly responsible for DCAD's cadastral database development, standards and base mapping that is based on 0.5-meter digital orthophotography. The consortium acts as a mentor for entities developing data to be shared among members. This pooling of GIS data produces useable coverages that have been developed on the same mapping base. Consortium members have access to all of the data produced by the participants.

3. Networking

The existing 10 Based T lines were abandoned and an RFP was released for a 100 Base T (Cat. 5) networking system with routers, hubs and the installation of a T-1 line. The 100 Base T networks sped up the daily workflow, while allowing for increased server backup capabilities. The T-1 line was instrumental in opening the District to the Internet and for allowing an accessible, safe and fast avenue to send GIS data to the North Texas GIS Consortium's data warehouse. The network hardware also allowed the GIS and the legacy LAN to communicate and eventually become one network under the same domain. It is hoped that this more robust network will allow traffic to flow bi-directionally with our IBM 9000 series mainframe computer, where the bulk of the "flat file" data is currently held. Since the goal of the District is to have one workstation perform all tasks, this networking starts DCAD down that road.

4. Staffing and Consultant Alterations

The training of manual drafters in the use of GIS seemed an obvious course of action. These drafters knew the ownership, platted, split, chain and new account procedures and had been performing these tasks for years. It seemed cost effective to keep them in place while transitioning them into the digital realm. They were given instruction in the PC operating system, ArcInfo, training in (COGO) Coordinate Geometry and they helped the GIS staff develop a custom maintenance AML for their use.

The GIS Division originally utilized Esri's technical assistance in the development of the system as a whole. That role has been developed into a partnering relationship, where the Esri technicians assist DCAD GIS staff members with Esri products. They also assisted in the planning of hardware/software upgrades, consulted in the direction of the industry and help the GIS staff in the migration towards Visual Basic, Map Objects, Internet Map Server, relational databases and education. This relationship has been invaluable to the success of the project.

The GIS division decided to abandon the idea of converting the cadastral data in-house as too expensive and time consuming. The advent of prison digitizing industries seemed repulsive to DCAD at first. But, being a publicly funded entity, we soon realized we could benefit from the special relationship we had as a quasi-governmental agency to the prison digitizing industry. They could only serve governmental entities and at a rate which was far below any other. Upon further scrutiny, it was decided to have the Mapping Unit at the Texas Department of Criminal Justice (TDCJ - Ferguson Unit) digitize all DCAD paper maps and rectify them to the Consortium base data. With assistance from the City of Dallas who previously had their maps digitized by the TDCJ, we provided a level assignment sheet for them to produce CAD drawings of our maps. These CAD drawing would then be converted into ArcInfo format. It was further decided to have a third party convert, append and finalize coverage maps. DCAD released a RFP for conversion services and a contract was awarded to Geo Info Systems, Inc. Geo Info Systems, Inc. are currently appending, producing the appropriate coverages and attaching ownership data.

B. Data Implementation Strategies

The procedure of attaching meaningful data onto dumb digital maps is something all GIS data developers contend with, sometime in their career. Plat dimensionality, ownership data and other cadastral information is very difficult to research and even harder to attach. Once the paper maps have been digitized and appended together, the tasks of following the standards and producing a useful GIS have just begun. The GIS staff, which consists of three persons, attempted to follow the database design and develop methods for automating data entry.

1. Data Structure

Since 1984, the Drafters, who reside in the Property Records Division, have been drawing plat maps, subdivisions, splits/chains and ownership changes on paper or linen maps. In the course of maintaining the property records, standards pertaining to account creation were produced that incorporated several geographic features. Property accounts were coded by a two-digit city number, a five-digit subdivision number, a three-digit block number, a three-digit lot number and an extra four-digit split/chain number.

a. Account Number Technique

Each city limit coverage was intersected with their corresponding parcels, attaching a two digit city code to the polygon attribute table. Subdivision boundary covers were produced from the paper plat maps. A five-digit subdivision number was attached to each parcel polygon attribute table, either by intersect or by 'heads-up' digitizing. Each block was selected, using the 'select polygon' command in ArcEdit. The three-digit number was attached by the moveitem command to each block, attaching the block number in the polygon attribute table. The individual lot numbers resided as anno.igds in the ownership coverage.

The lot numbers/letters (anno.igds) were brought into ArcView. The anno.igds were run through an Avenue script that exports them into a shapefile. The shapefile, which consists of the lines, are intersected through the ownership parcels. This intersection attaches the lot numbers/letters into the polygon attribute table. The resulting lines inside of each polygon are then deleted. An item is added to the polygon attribute table as a character field. The final step is to concatenate the character field that was just added. The character field is concatenated from city, subdivision, block and lot. Four zeros are added to the concatenated item to simulate the last four split/chain numbers. The ownership flat file is then either related or joined with the polygon attribute table producing about a ninety-percent match.

b. View and Attach Technique

The ten-percent remaining unmatched files can be populated with flat file data by the view and attach method. This method starts by bringing up both flat file and digital parcel data on the same screen. The GIS operator then simply finds the corresponding flat file with the correct parcel and adds the account number to the parcel. The cut and paste tools can speed up this technique.

c. Look up Technique

The final and more laborious method is the look up technique. This technique starts out with paper copies of the parcels that did not match using the previous two methods. Then each individual parcel is researched in the flat file database for geographic parameters. Once an account number is discovered, it is then written on the paper copy. A GIS operator then transfers the account numbers from paper to digital format. At DCAD there will be between 60,000 and 70,000 accounts that must be attached in this manner.

Conclusion

The road to a successful cadastral GIS has been paved by previous GIS pioneers. If one can glean the historical techniques these established GIS groups have documented, planning and implementation of a new cadastral GIS is reduced to picking GIS items off a GIS menu. A cadastral project can flow smoothly by planning your procedures and standards (National Research Council, 1983), discover the user requirements and future plans of the organization (Esri, 1996), analyze the hardware/software variables, become a master of your software and utilize the previous experiences of other GIS specialists in your field. Continued success after the implementation stage will rely on the degree of the GIS team's knowledge in technologic advances, software sophistication and contact with their users.

References

Esri, Managing a GIS, Environmental Systems Research Institute, Inc., Redlands, CA:Esri Educational Services, 1996.

Larsson, Gerhard, Land Registration and Cadastral Systems: Tools for Land Information and Management, Longman Group UK Limited, 1991.

National Research Council, Procedures and Standards for a Multipurpose Casdastre, Washington, D.C., National Academy Press, 1983.

Acknowledgments

I wish to thank the following people for their contributions to DCAD's GIS Division:

Gary Penny - City of Dallas, Casey Gardner - City of Dallas, Henry Hagemeier - Esri, Dr. Ron Briggs - University of Texas at Dallas, Leann Gilley - Geo Info, Inc., John Hunt - NCTCOG, Paul Lauder - DCAD, Robert Hoffpauer - DCAD

Stuart Murchison
Manager of GIS, DCAD
murchisons@dcad.org