What does Mapping/GIS have to do with my property value?

In order to appraise property at fair market value it must first be located and identified. Locating land is fundamental to the tax mapping process.  Once land is located it must also be given its own unique "identifier".  This "identifier" is known as a parcel identification number (PIN) and works like a social security number, it identifies a parcel into perpetuity.  A good land description will permanently and distinctly locate one and only one individual parcel of land. Written land descriptions may be based on US Public Land Survey System (section, township, range) a metes and bounds description or a coordinate grid system.  This system is based on the idea of parallels and meridians that circle the globe.  The equator and all horizontal lines north and south of it are known as parallels.  The Vertical lines converge at the north and south poles are known as meridians.

The US Public Land Survey systems also has its    special meridians and parallels throughout the United States.  The meridians are known as "principals" meridians.  Each principal meridians has a parallel.  These are know as "base lines".  The points where the two meet are known as initial points. Another set of lines is established at 24-mile intervals north and south of the base line and at 24 mile intervals east and west of the principal meridian.  The east-west lines are called standard parallels or corrections lines, they are one continuous, uninterrupted line.  The north and south lines, called guide meridians, are not continuous throughout their length.  Because meridians converge as they get closer to the poles, they must be broken at the base line at each standard parallel.

The guide meridians and standard parallels form a 24-mile square.  Each of these 24-mile squares are divided into sixteen small units of land called townships.  A township is, as nearly as possible, six miles by six miles square.  A row of townships extending north to south is called a "range" and a row east to west is called a "tier".  Each township is further divided into 36 one-mile square areas called "sections".

Sections can be subdivided as well.  The quarter section (160 acres, 1/2 mile square), the half-quarter or eighth sections (80 acres, 1/4 mile by 1/2 mile), and the quarter-quarter or sixteenth section (40 acres, 1/4 mile by 1/4 mile).  The quarter-quarter section is the minimum legal subdivision under the general land laws but it is common to divide the subdivision further for description purposes.

Graphic land descriptions are based on the recording or filing of plats.  These descriptions are known a "recorded map descriptions" or "legal recorded plats".  Record map descriptions are descriptions of parcels with reference to lot numbers and/or block numbers.

The Revenue Commissioner's office also uses aerial photographs to locate and identify property.  There are several types of aerial photographs listed below:
**Aerial Photographic Enlargement:  is nothing more than a "blown-up" photograph.  Neither tilt nor relief displacement are removed for these photographs.  Because of this, you will not be able to make accurate measurements from the photo or from maps made from it.  These photos are helpful for inventory of parcels and locating structures.
**Rectified Aerial Photographs:  is one in which distortions causes by tilt and yaw of the airplane have been removed.  The rectification process is accomplished by projecting the photo image onto a flat surface that is tilted to eliminate the tip and tilt of the aircraft.  The objective is to project the image back to its correct sharp and scale.  Although relief displacement is not removed from rectified photographs, this type of photography provides acceptable accuracy for assessment mapping in areas of relatively flat terrain.
**Ortho-photographs:  look a lot like the other two types of aerial photographs.  However, it has the accuracy of a map drawn from ground survey information because tilt and relief displacement have been eliminated.  Measurements of a land surveyor on the ground should "fit" when plotted on a true-to-scale ortho-photograph.  Distances and area calculations on an ortho photograph are usually extremely accurate, and property lines will correspond closely to physical features.
**Digital Ortho-Photographs:  is an ortho photograph scanned or created in a digital format.  These have the same accuracy as ortho photo sheets, but also provide us a method to lay property lines or any other data over the photo.

GIS, Geographic Information Systems:
GIS is a computer technology that combines mapping and information stored as data to generate maps and reports, to provide a planned and systematic approach to collecting and managing location-based information, and to enable elected and appointed officials to improve planning and decision making.  Through the integration of data and maps, the decision environment is vastly improved for decision makers.  A GIS uses geographic location to relate otherwise disparate date.

In 1993, the Montgomery County Appraisal Department, under the direction of Tommie Miller, Chief Appraiser embarked on the task of implementing a Geographic Information System (GIS).  The foundation for which all future graphic data would be built upon was created in the form of Digital Ortho Photography.  Production of the photo imagery began by placing 392 Global positioning Stations (GPS) monuments throughout the county, and using GPS receivers, X, Y and Z coordinates were gathered for each monument.  Over 100 of these monuments were first order monuments and were "Blue Booked" with the US Geological Survey office.  The monuments were then "Paneled" to make them identifiable on the photography and on February 25,  1994 the photography was flown.  The final product consists of digital imagery with pixel resolution of 0.5 feet for the 50 and 100 scale mapping, 1 foot for the 200 scale mapping and 2 feet for the 400 scale mapping.

The county was then mapped using coordinate geometry and best-fit methods by gathering the information from all of the recorded plats and deeds of record and constructing them on top of the photography.

Montgomery County's GIS is enterprise wide, uses include:  County for parcel mapping, E911 (for situs), in engineering for the right-of-way management, etc.; at the City for planning and development, long range planning, districting (garbage truck routing, police & fire routing, etc.); the Water Works for facilities management, engineering and construction of water & sewer lines, etc.; the School Board for districting, bus routing, and facilities management.