Oklahoma County Assessor
Mapping/GIS Department

Locating land is fundamental to the tax mapping process.  Once land 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 Oklahoma, land is described by written descriptions or legally recorded plats.

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 Oklahoma, land described using this system is referenced to either the Indian or the Cimarron Meridians.  We also have the original 1905 Government Lot Survey Books available.

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.   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 descriptive purposes.

Graphic land descriptions are based on the recording or filing of maps.  These descriptions are known as "recorded map descriptions" or "legally recorded plats".  Record 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 now a Reality.....

GIS or Geographic Information Systems (GIS) has become a reality in our office. The initial base maps are complete, covering all 720 square miles of Oklahoma County.  We are now maintaining and constantly updating new plats, sub-divisions and parcel splits into our digital maps.  A new law took effect this year requiring developers to submit digital plats or sub-divisions in State Plane coordinates, this will help streamline the process of integrating these plats with our existing digital maps.

We can now connect with our CAMA (Computer Automated Mass Appraisal) system. We are able to retrieve data from the parcel or account number as you view the map on the same screen. We are also able to search the data on the CAMA system and produce the information on a map.  This can now be done both internally and on our GIS website.

We also have new color digital aerial photographs, some of the most accurate aerial photographs available, for all of Oklahoma County which were taken in 2003, 2004, 2005 and 2006.   We can overlay the digital maps on the color aerials to help determine improvements to the property, land use, and other important changes.  The file formats consist of the original TIF's as well as the converted Mr. SID files including one large mosaic SID file of the entire county. 

Our mapping website features the digital maps and color aerial photos. Searches can be performed by owner name, physical address, or account number. Centerline data was also added to search by street intersection. We will also be able to identify owners by buffer zones, like the 300 foot radius to notify property owners required for zoning changes. We also have school districts, city boundaries, political districts as well as flood plain and contour data.  Queries can be made by owner name, legal description, physical address, or account number.  Centerline data is also available to query by street intersection. Upgrades to this site will be made on a continuous basis.
 

Flood Hazard Mapping...Flood Hazard Zone Designations
Per FEMA website taken 1/25/2012  -  Click here to access the FEMA Website

The zone designations shown on the FIRMs are defined below.

Zone A
Zone A is the flood insurance rate zone used for 1-percent-annual-chance (base flood) floodplains that are determined for the Flood Insurance Study (FIS) by approximate methods of analysis. Because detailed hydraulic analyses are not performed for such areas, no Base Flood Elevations (BFEs) or depths are shown in this zone. Mandatory flood insurance purchase requirements apply.

Zone AE and A1-A30
Zones AE and A1-A30 are the flood insurance rate zones used for the 1-percent-annual-chance floodplains that are determined for the FIS by detailed methods of analysis. In most instances, BFEs derived from the detailed hydraulic analyses are shown at selected intervals in this zone. Mandatory flood insurance purchase requirements apply. AE zones are areas of inundation by the 1-percent-annual-chance flood, including areas with the 2-percent wave runup, elevation less than 3.0 feet above the ground, and areas with wave heights less than 3.0 feet. These areas are subdivided into elevation zones with BFEs assigned. The AE zone will generally extend inland to the limit of the 1-percent-annual-chance Stillwater Flood Level (SWEL).

Zone AH
Zone AH is the flood insurance rate zone used for areas of 1-percent-annual-chance shallow flooding with a constant water-surface elevation (usually areas of ponding) where average depths are between 1 and 3 feet. BFEs derived from detailed hydraulic analyses are shown at selected intervals within this zone. Mandatory flood insurance purchase requirements apply.

Zone AO
AO zones are areas of sheet-flow shallow flooding where the potential runup is less than 3.0 feet above an overtopped barrier crest (ΔR<3.0 feet). The sheet flow in these areas will either flow into another flooding source (AE zone), result in ponding (AH zone), or deteriorate because of ground friction and energy losses and merge into the X zone. AO areas are designated with 1-, 2-, or 3-foot depths of flooding.

Zone AR
Zone AR is the flood insurance rate zone used for areas protected by flood-control structures, such as levees, that are being restored. FEMA will consider using the Zone AR designation if the flood protection system has been deemed restorable by a Federal agency in consultation with a local project sponsor; a minimum level of flood protection is still provided to the community by the system; and restoration of the flood protection system is scheduled to begin within a designated time period and in accordance with a progress plan negotiated between the community and FEMA. Mandatory purchase requirements for flood insurance apply in Zone AR, but the rate will not exceed that of an unnumbered Zone A, if the structure is built in compliance with Zone AR floodplain management regulations.

For floodplain management in Zone AR areas, the property owner is not required to elevate existing structures when making improvements. However, new structures must be elevated (or floodproofed for nonresidential structures) so that the lowest floor, including the basement, is at least 3 feet above the highest adjacent existing grade, if the BFE does not exceed 5 feet at the proposed development site. For infill sites, rehabilitation of existing structures, or redevelopment of previously developed areas, there is a 3-foot elevation requirement regardless of the depth of the BFE at the project site.

The Zone AR designation will be removed and the restored flood-control system will be shown as providing protection from the base flood on the National Flood Insurance Program (NFIP) map when the restoration project is complete and all the necessary data have been submitted to FEMA.

Zone A99
Zone A99 is the flood insurance rate zone used for areas within the 1-percent-annual-chance floodplain that will be protected by a Federal flood-protection system, where construction has reached specified statutory milestones. No BFEs or depths are shown in this zone. Mandatory flood insurance purchase requirements apply.

Zone D
The Zone D designation is used for areas where there are possible but undetermined flood hazards. In areas designated as Zone D, no analysis of flood hazards has been conducted. Flood insurance is optional and available, and the flood insurance rates for properties in Zone D are commensurate with the uncertainty of the flood risk.

Zone V and V1 - 30
Zone V and V1 - 30 designation is for coastal areas with a 1-percent or greater chance of flooding and an additional velocity hazard associated with storm waves (wave action). Because detailed hydraulic analyses are not performed for such areas, no BFEs or depths are shown in this zone. Mandatory flood insurance purchase requirements apply.

Zone VE
VE zones are coastal high hazard areas where wave action and/or high-velocity water can cause structural damage during the base flood. They are subdivided into elevation zones with BFEs assigned. VE zones are identified using one or more of the following criteria for the base flood conditions:

1. The wave runup zone occurs where the (eroded) ground profile is 3.0 feet or more below the 2-percent wave runup elevation
2. The wave overtopping splash zone is the area landward of the crest of an overtopped barrier, in cases where the potential 2-percent wave runup exceeds the barrier crest elevation by 3.0 feet or more(ΔR>3.0 feet). (See Subsection D.2.8.2.)
3. The breaking wave height zone occurs where 3-foot or greater wave heights could occur (this is the area where the wave crest profile is 2.1 feet or more above the total stillwater level).
4. The primary frontal dune zone, as defined in 44 CFR Section 59.1 of the NFIP regulations.

For the Pacific Coast only:

5. The high-velocity flow zone is landward of the overtopping splash zone (or area on a sloping beach or other shore type), where the product of depth of flow times the flood velocity squared (hv²) is greater than or equal to 200 ft³/sec².

Zone B and X (shaded)
Zones B and X (shaded) are areas of 0.2-percent-annual-chance floodplain, areas of 1-percent-annual-chance (base flood) sheet flow flooding with average depths of less than 1 foot, areas of base flood stream flooding with a contributing drainage area of less than 1 square mile, or areas protected from the base flood by levees. No BFEs or depths are shown in this zone, and insurance purchase is not required

Zones C and X (unshaded)
Zones C and X (unshaded) are flood insurance rate zones used for areas outside the 0.2-percent-annual-chance floodplain. No BFEs or depths are shown in this zone, and insurance purchase is not required.

Acreage and Proportionate of the Soils
Provided by USDA - Natural Resources Conservation Service Data Version Date 04/22/2004

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