Landbase Development
Landbase Categories
Landbase mapping generally falls into one of two categories: cadastral or image-based.
Cadastral maps show lot, parcel, and ownership lines in vector format and are generally
used by property appraisers. Image based mapping is usually produced through
photogrammetric methods and may include either linework or photo images. Both methods
produce consistent map products that conform to predetermined standards.
Existing Landbase Sources
It is always wise to look for any existing landbases that cover all or part of the area(s) for
which you need mapping which can be used. This search should begin within your own
organization to see if the landbase in your current facility records can be used or if a
landbase is available from another department. Often you can acquire the right to use
existing landbases for a fraction of the cost involved in producing new mapping. In addit
ion, these existing landbases will be available to your project much sooner.
If there is nothing available within your organization, you may find that a utility or
communication company in your area may have a landbase, that will meet your
requirements. Sometimes you will find that a governmental organization will have
something available that will meet your needs. The United States Geological Survey
produces quadrangles at a scale of 1"=2,000' which have an accuracy of plus or minus 50'.
Unfortunately these maps may not have been updated for the past five to ten years.
You may find commercial off the shelf (COTS) mapping that will meet your needs. These
landbases will often contain address information. Some users have assembled hybrid
landbases by obtaining the right to use information such as the address data from one of
these sources and then conflating that information to a more accurate street centerline
landbase. The owner of the COTS data may be interested in trading data for improved
positional accuracy.
When evaluating existing landbases, always watch to see that by using this source you are
not be making a trade-off that will compromise your applications. By sharing the use of an
existing landbase you may be able to share the cost of maintaining it, thereby resulting in
long term operating savings for your organization.
New Landbase Mapping
Developing new landbase mapping offers the maximum flexibility in design. Accuracy and
content can be customized to meet your specific requirements. This new mapping can be
cadastral based, imaged based, or a combination of both.
Cadastral
Cadastral maps generally show features that are not clearly identifiable on aerial
photography. Cadastral maps (often referred to as “tax maps”) showing right-of-way lines,
legal lot and parcel lines, ownership lines and easements are based on government records
such as legal deeds. In some cases, the cadastral maps become the legal property record.
Cadastral maps are usually compiled either by the use of coordinate geometry software
(COGO) or by using “best fit” techniques. The horizontal accuracy of a cadastral map is
determined by the control method used. The control may be based on photogrammetrically
compiled data or it may be based on a geodetic control network. In the western United
States, it is common to find cadastral mapping based on the Public Land Survey System
(PLSS) using the township and range system and section corners.
