Center for Geographic and Statistical Analysis

The Center for
Geographic and Statistical Analysis





Parcels can form the basis of a GIS but they are often difficult to map and maintain. The level of accuracy is the most important factor in determining the method of mapping parcels and the costs.


Mapping parcels is possible by scanning existing paper assessor maps. This is the easiest, but quite a bit of accuracy is lost. The most accurate, and therefore expensive, method is to draw the lines using survey coordinates (coordinate geometry also known as COGO). It is possible to map parcels using an intermediate method, perhaps initially scanning available paper maps then over time use COGO to improve the accuracy.

Initial Cost

The cost of creating a parcel coverage depends on the accuracy required. A technician might create five parcels an hour using the COGO method, but this assumes all the surveys, plats, and other legal information is readily available. Inevitably conflicts will occur, neighboring parcels might have unwanted gaps between them or they might even overlap. Resolving these errors adds costs.


Once a parcel coverage is built, maintenance is generally straight-forward. A GIS application can automate updating and improve the accuracy of any new parcels. A GIS or cadastral technician would maintain the parcels using a mouse instead of pen and ink. The technician would use a set of GIS tools built specifically for maintaining parcels. The technician is thus free to concentrate on updating parcels and doesn't have to know anything about GIS programming.


Creating and maintaining parcels using a GIS is the most efficient way to keep property information updated and secure. A stack of paper maps is prone to damage or loss. Computerized data is routinely backed up and kept secure. How much would it cost you to recreate all your paper parcel maps in the event of a catastrophe?


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