GIS (Geographic Information Systems)
A GIS combines layers of information about a place to give you a better understanding of that place. What layers of information you combine depends on your purpose—finding the best location for a new store, analyzing environmental damage, viewing similar crimes in a city to detect a pattern, and so on. This technology is very helpful to use in Assessment of real and personal property.
It is helpful to know geography and mapping terms to understand GIS.
If you can identify a location on the surface of the earth you can then
associate information to that geographic location. GIS allows layers of
information to be visually mapped and analyzed.
|Locating specific areas of land is fundamental to the tax mapping process. Once a specific area is located it must also be given its own unique "name". This is called parcel identification. A good land description will permanently and distinctly locate one and only one individual parcel of land. In Salt Lake County, land is described by written descriptions or legally recorded plats.|
The Salt Lake County Assessor’s Office receives this parcel information from the Salt Lake County Recorder’s Office.
Written land descriptions may be based on the rectangular survey system (also known as the township and range system), a metes and bound description or a coordinate description 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 which converge at the north and south poles are known as meridians.
The rectangular survey system also has its own special meridians and parallels throughout the United States. The meridians are known as "principal" meridians. Each principal meridian has a parallel which goes with it. These are known as "base" lines. The points where these two meet are known as initial points. In Salt Lake County, land described using this system is referenced Salt Lake Base and Meridian
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 and at each standard parallel.
The guide meridians and standard parallels form a 24 mile square. Each of these 24 mile squares is divided into sixteen smaller units of land called townships. A township is, as nearly as possible, six miles by six miles. Each township is given a range which numbers it in ascending order from the meridian. For example T1S, R2E would be the first township south of the base line and the second township east of the meridian. Each township is further divided into 36 one mile square areas called sections.
Graphic land descriptions are based on the recording or filing of maps. These descriptions are known as "recorded map descriptions" or "legally recorded plats". Recorded map descriptions are descriptions of parcels by reference to lot numbers (or letters) and/or block numbers (or letters), and name or numerical designation given to a recorded or filed map.
The County Assessor’s Office also uses aerial photographs to locate and identify property. There are several types of aerial photographs as 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 of from maps made from it.
These photos are helpful for inventory of parcels and locating structures.
Rectified Aerial Photograph - is one in which distortions caused by tilt displacement have been removed. The rectification process is accomplished by projecting the photo image onto a flat surface that is tilted to eliminate the original tip and tilt of the aircraft. The objective is to project the image back to its correct shape 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 can be viewed and manipulated on the computer, with the capability to zoom in or out. This also provides us a method to lay property lines or any other data over the photo.
GIS or geographic information systems is well on it’s way to becoming a reality for our office. Many projects are underway in retrieving data from the CAMA (computer automated mass appraisal) system referred to as the SIGMA database. This allows staff to query the data and produce information visually on a map. This is helpful in analyzing the data necessary in the assessment process, and in processing work in a more efficient and effective manner improving the quality of the assessments. The Salt Lake County Assessor’s Office uses GIS software developed by ESRI
Metadata for GIS Maps- Metadata is data about the data
GIS Map Image Gallery- View maps in the Recorder’s Gallery
The Salt Lake County Complex Image
Salt Lake County Topographic Image
GIS Map - Parcel Layer ViewerThe map you will initially view is to the full extent of Salt Lake County. To zoom in to see the parcel layer use the magnify tool - an icon of a circle with a + sign on it. This is located on the left side of the map. By using this tool you will be able to view parcel boundaries, parcel numbers, and streets.
- 1. Click on the magnify glass icon
- 2. Move your cursor to the area of the map you want to see up close.
- 3. Click on the mouse, hold down, drag to create a rectangle shape,
release the mouse button
(Step 3 may be repeated as needed to get to the parcel (s) you want to view)