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General Guide for Tax Mapping in New York State


  1. Introduction
    1. Tax map preparation and maintenance
    2. Use of a tax map
  2. Tax map system 
    1. Tax map scales, symbols, lines and dimensions
    2. Parcel numbers and coordinate locator numbers
    3. Effective tax map use
  3. Index system
    1. Types of index cards (manual system)
    2. Mechanized (computer) cross reference index file
    3. Index maps
  4. Maintenance system
    1. Maintenance system description
    2. Assessor's part and use of the maintenance system
  5. Digital tax map conversion
    1. Selecting a system
    2. Cost and conversion methods
    3. Map maintenance
  6. Appendix

Tax mapping: Foreword

Perhaps the most essential of all assessment tools is an adequate tax map reflecting the size, shape and locational characteristics of each parcel of land in the assessing unit. The tax map is a graphic display of each assessing unit's land inventory and as such is the major backup to the assessment roll. The working copy of the tax map used by the assessor can be utilized to record and analyze property transfers, to record topographical and other features pertinent to the valuation of land and in the development of land value maps. An adequate map is so fundamental to the valuation process that it is doubtful that any reasonable degree of assessment equity can exist in an assessing unit without an adequate tax map.

The Assessment Improvement Law (Laws of 1970, Chapter 957), mandated that each county prepare a tax map prior to October 1979. This same law prescribed that the State Board of Real Property Services will develop rules and regulations for the preparation of these tax maps and assigns to County Directors of Real Property Tax Services important duties relating to tax map preparation and maintenance.

This manual was originally prepared in 1971 as a guide to the assessor and county director of real property in the use of tax maps. It has been reissued several times since. The approved tax map you already have may vary slightly from the descriptions contained in this manual.

1. Introduction

This material has been prepared as a guide to local assessors in the use of a tax map. Definitions of terms in tax mapping are included in the appendix.

A tax map is a special purpose map, accurately drawn to scale showing all the real property parcels within a city, town or village. These maps are used to locate parcels and obtain other information required in assessment work. As changes take place in ownership, size, or shape of the parcels, the tax map system must be updated. 

A. Tax map preparation and maintenance

The initial preparation and continued maintenance of tax maps are the responsibility of the Real Property Tax Service agency of the county or assessor where applicable. The cooperation and assistance of assessors are essential in a successful Tax Mapping Program.

  1. Tax map preparation

    Data which is obtained from state, federal, county and local government departments must be located and analyzed for use in tax map preparation.

    A base tax map is prepared using aerial photographs specifically created under controlled conditions. The aerial photographs clearly show all geographical features such as streets, roads, lakes, streams, railroad and utility lines, as well as property occupancy lines when they are well defined on the ground. Points of reference on the ground will have been prominently marked so as to provide check points on the photography. This photography is used as the foundation for preparing base manuscripts and includes features shown thereon that will assist the plotting of parcels. The base manuscripts are the basic maps from which the final tax map is prepared. All deeds or other instruments of conveyance are examined to determine the ownership of each parcel to be plotted on the maps.

    A tax map is generally drafted on map sheets 30 inches high by 42 inches wide. The parcels are delineated on the tax map using the data obtained through deed research and plotting. Every parcel on a tax map is assigned a parcel number and a coordinate locator number. An index map is prepared showing the area covered by the tax map in a city, town or village. When the tax map is completed, the map sheets may be bound together in sets or otherwise filed by the city, town and village. The original maps remain where the maintenance is to be done. Prints are provided to the assessors. According to the State Board's Rules for the Preparation and Maintenance of Tax Maps for Real Property Assessment and Taxation Administration, the assessor's copies of the tax map are a public record and must be displayed and made available for inspection by the public.

  2. Tax map maintenance

    Once a tax map is completed, it must be kept up-to-date. Revisions are required when there are changes in parcel size or shape. The same data and methods are used during the maintenance process as were used in the original work.

    The formation of new subdivisions generally requires the addition of many new parcels to the tax map. If many new parcels are added, a new map sheet may have to be prepared for that area.

B. Use of a tax map

A tax map is primarily used by local governments to maintain a current inventory of all parcels in a city, town or village.

  1. Property identification

    The size, shape and dimensions (or acreage) or a parcel may be found on a tax map. Cross-reference through the parcel number to matching index cards or computer listings provides still other parcel information. The parcel numbering system provides a history of the way parcels are subdivided.

  2. Assessment purposes

    A tax map reduces the amount of work involved in assessment. Parcels are quickly located and additional information is easily obtained from the cross-reference index file.

    In a reassessment program, tax map parcels are easily grouped on the map for delineation of valuation influences.

    A tax map even simplifies the preparation of the assessment roll itself. Parcel identification numbers on an approved tax map constituted a legal description of a parcel on an assessment roll and are concise and accurate.

2. Tax map system

A county tax map covers all the cities, towns and villages in the county. Each set of maps for a city, town and village is complete within itself. Each map sheet of a tax map covers one specific area, called a section. Every section is assigned a section number. The index map shows, and identifies, the areas covered by each of the section maps of that municipality.

Parcels delineated on a tax map are identified by numbering systems. These numbers constitute a description for each parcel assessed and are used to locate the matching index file data for the parcel. The index file contains important data about the parcel and references to still further information.

  1. Tax map scales, symbols, lines and dimensions

    Each map has a legend at the bottom of the sheet that explains many of the lines and symbols used on the map. An explanation of some of these items follows:

    1. Scales and Dimensions

      Areas with many small parcels are generally plotted using a large scale, such as 1 inch equals 50 feet. Cities and villages are generally mapped at a scale not smaller than 1 inch equals 100 feet. Where the area being mapped contains relatively few small parcels, the scales used are generally 1 inch equals 200 feet or 1 equals 400 feet. Dimensions are given for each boundary of parcels of less that one acre. These dimensions are obtained from property deeds and other records. If the data are not available from these sources, the dimensions are scaled. In this case the dimensions are labeled with an (s) after the dimension.

      Parcels of one acre or more need show only the road frontage dimensions. The parcel acreage must also be given. If the acreage is a calculated value, the acreage figure is followed by a (c). See Exhibit #1 in appendix.

    2. Lines and Symbols

      Lines and symbols are used on the tax map to indicate boundaries and other distinguishing features. The legend shown on each map will explain the lines and symbols being used. A typical legend is shown in Exhibit #2 in appendix. Depending on the mapper or local circumstances, other lines and/or symbols may be employed.

  2. Parcel numbers and coordinate locator numbers

    Parcel numbers and coordinate locator numbers are required for every parcel of property.

    1. Parcel numbers 

      An individual parcel number is assigned to each parcel in the county when the map is prepared.

      1. Generation of parcel numbers

        In reading the next two paragraphs, please refer to Exhibits 2, 3A, and 3B in appendix.

        All parcel numbers consist of three basic parts: the section number, the block number, and the lot number.

        The section numbers are based on county modular units. Generally, every county is divided into modular units, 8,000 feet by 12,000 feet. The 12,000 foot dimensions lie along the north and south boundaries and the 8,000 foot dimensions lie along the east and west boundaries of these modular units. These modular units correspond to a map scale of 1" = 400' and will measure 20" x 30" on each section map.

        Each of the modular units is assigned a section number. The numbers start with one and increase consecutively from left to right across each row of modular units in the county starting with the top row. You will note that the example county in Exhibit 3A consists of 43 modular units. You will note also that certain modular units cross town and village lines. Modular unit boundaries do not necessarily coincide with city, town and village boundaries. In Exhibit 3A note also the symbols used for village, town and county boundaries, as taken from Exhibit 2.

        When a scale larger than 1" = 400' is required, the section number is followed by a two-digit suffix number which indicates the scale and the area within the modular unit that is mapped at the larger scale. (Refer to Exhibits 3C and 3D in appendix). Exhibit 3C shows the area covered by the modular unit at larger scales of 1" = 200', 1" = 100', and 1" = 50'. Notice that at 1" = 200' it requires four sections to cover the same area shown at 1" = 400' (at 1" = 100' it requires 16 sections, at 1" = 50' it requires 64 sections). Exhibit 3D shows the actual suffix numbers to be used with the 1" = 400' section number when larger scales of mapping are used.

        Typical section numbers for a county originally divided into 1" = 400' modular units might look like the following:

        Example section numbers
        1" = 400' map: Section 10 10.0
        1" = 200' map: Section 12 12.04
        1" = 100' map: Section 15 15.16
        Portion of Section 15.16 at 1" = 50' 15.68

        Each section can be subdivided into blocks. Up to 99 blocks may be included in a section. Blocks are formed to provide less than 100 parcels in any block. The blocks are numbered consecutively starting with the number 1. The blocks are usually formed using natural boundaries such as roads, rivers, railroads or other prominent features. In many instances, however, arbitrary block boundaries are used.

        Lot numbers are assigned to each parcel in a block starting in the upper left portion of the block. They are numbered consecutively starting with number 1, continuing in a clockwise direction, whenever practicable, around the entire block. A complete parcel number might look like 10.16-1-24. If the map scale was changed to 1" = 50' in that area, the new parcel number might look like 10.68-1-24.

      2. Locating a parcel on a section map
        1. The section number is obtained from the title block in the legend at the bottom of each section map, usually in the right corner.
        2. The block number is usually an encircled number and is placed on the map at about the center of the block. However, check the legend for the correct symbol, as it may vary from mapper to mapper.
        3. The lot number consisting usually of one or two digits is shown within the lot boundaries.
      3. Subdivision or combining of parcels

        When parcels are divided, new parcels are formed known as subdivisions. The subdivisions carry the original lot or parcel number, and a suffix starting with the number 1 is added. If part of the parcel, prior to subdivision, has been retained by the original owner, it carries the suffix 1. Where an original parcel is extensively altered, it will be necessary to renumber the parcels. Refer to Exhibit #4 for an example.

        The same general procedure applies to parcels that have been combined, possibly with slight variations.

    2. Coordinate locator numbers

      A unique number called a coordinator is assigned to each parcel of land within an entire county. By unique, we mean that this number will not be duplicated within a county. This number is not intended for manual use but will be utilized in a computerized environment to help support new valuation and assessing techniques for local governments.

      1. Origination

        The mapper generates the coordinate locator number. It is simply a measurement of the parcel's location from a given point added to the constant readings at the given point in the New York Coordinate System.

        The first set of digits shows the final easterly reading. The second shows the final northerly reading. See Exhibit #5.

        The term coordinate locator number means an east reading and a north reading, in feet or meters, taken from the point of origin of the appropriate zone of the New York Coordinate System to the visual center of each land parcel.

      2. Subdivision

        When parcels are subdivided, a new coordinate locator number must be generated for each of the subdivided parcels. Each of the new coordinate locator numbers must be different from the number used for the original parcel. Refer to Exhibit #6 for an example.

  3. Effective tax map use

    To obtain maximum benefit, a tax map must be used to the greatest extent possible. When this is done, considerable time and effort in all phases of assessing work will be saved. The assessor may wish to have copies of section maps reduced in size for field use. Parcel numbers and coordinate locator numbers are required for every parcel of property. 

    1. Location and shape of parcels 

      Knowing the location and shape of parcels is a great assistance during any assessing program. Since parcels can be located rapidly from the maps, and further data can be obtained from the associated index system, much valuable time can be saved. The parcels to be assessed may be conveniently grouped for efficient coverage.

    2. Relationship of surrounding parcels

      The relationship of parcels surrounding a given parcel is graphically shown on a tax map.

    3. Grievance day

      On grievance day, the tax map is a valuable aid in discussions with taxpayers. The tax map gives a picture of the properties in question and other related parcels.

    4. Use with index system

      A parcel may be located in the cross-reference index files by parcel number or by surname of owner.

      Part of the index system is an index map which shows the coverage of each section map within a city, town or village.

3. Index system

The index system consists of a series of cross-reference index data files and index maps for each city, town and village. Both tools facilitate locating parcels on the section maps and refer to other related parcel information.

In some jurisdictions, the cross-reference index data are still manually entered on cross-reference index cards. In this type of setup, the index cards are generally maintained by each assessor and County Real Property Tax Service Agency in two sets: usually one set is filed numerically by parcel number and the other set is filed alphabetically by surname of the owner.

In a growing number of jurisdictions, the cross-reference index data are captured on IBM cards, magnetic tape or disc, and maintained by the County Real Property Tax Service Office. Computer printouts are supplied to the individual local assessors for their day-to-day use and maintenance. New copies of the computer printouts are supplied periodically as required.

The index maps serve as a key to locate the various section maps in a municipality.

  1. Types of Index Cards (Manual System)

    In some index card systems there are two identical sets: one filed by parcel number and the other by owner's surname.

    Other systems use the numerical set as the master cards, containing all information. In such a system, the alphabetical cards merely refer to the matching card by parcel number.

    Minimum State Board requirements for index cards are given below.

    1. Numerical

      The numerical cards should provide for the following:  

      1. parcel number: section block and lot number.
      2. coordinate locator number.
      3. name of the city, town or village
      4. Physical location of the property, such as street number and name.
      5. Dimensions and/or acreage.
      6. Subdivision name, map reference, and lot number.
      7. If applicable, tract information showing the tract, lot, section, township and range.
      8. School and special districts.
      9. Parcel identification that existed prior to the development of the tax map. (The previous identification is essential to an orderly transition from an old system to a new system based on a tax map.)
      10. Information with respect to the owner includes the following: owner's names, mailing addresses, deed reference.

        All of this information can be shown on the index cards maintained in numerical sequence if 4 x 6 inch cards are utilized both front and back.

    2. Alphabetical

      Where the alphabetical set of index cards is not a duplicate of the numerical set, a single card may be used to list all properties owned by a single owner. In this case, the following information must be provided.

      1. Owner's name, with the surname being the prominent feature for filing.
      2. The complete mailing address of the owner.
      3. The name of the city, town or village.
      4. Property address.
      5. Parcel number.
      6. Deed reference - Liber and page.
      7. When the property is sold, there should be room provided on the card to indicate the new owner, the date sold, and the new deed reference.

  2. Mechanized (computer) cross reference index file

    In this type of arrangement, all the minimum State Board requirements for the numerical data are captured and stored in a master computer file. A printout can then be produced automatically, based on either a numerical or alphabetical sequence, because the numerical file duplicates all the information on the alphabetical file. An alphabetical listing, therefore, would list any and all parcels owned by any taxpayer in sequence according to surname, with all the data pertinent thereto.

    Note: The cross-reference data to be captured in either a manual or mechanized systems are those stated in the State Board requirements.

  3. Index maps

    The index maps for a municipality are at a smaller scale than the individual section maps. On each index map is found the outline of each section map in the municipality with its proper numerical designation. To assist in locating a particular section map, features such as major roads, streets, waterways and railroads are shown.

4. Maintenance system

Continued maintenance of the tax map and index system is necessary to keep both sets of records up-to-date. Without continued maintenance, the tax map and index system will rapidly become useless. County tax map systems approved by the State Board are required by statute to be maintained by the county. Prior to completion of a tax map project, the county director of real property tax services will provide assessors will explicit information as to how the tax map maintenance system will operate in their county. The following description is general in nature, pending issuance of specific instructions by the county director of real property tax services.

As changes occur in parcel size, shape or number, revision to the tax map and index file becomes necessary. The actual maintenance work is the responsibility of the county, except in a few designated counties where it is the specific responsibility of the individual assessors.

The assessors' cooperation and assistance are essential in the maintenance of the tax map as well as in the initial preparation of the tax map.

All tax map revisions and additions require changes to be made in the index system, but not all changes in the index system require tax map revisions.

  1. Maintenance system description

    1. Tax map maintenance

      Any changes in the boundaries of parcels, special or service districts or other features require tax map revision.

      1. Parcel Number

        Parcel numbers are changed whenever parcels are split or new parcels established. It is sometimes necessary to renumber all the parcels in the whole book.

      2. Coordinate locator number

        Subdivided parcels require new coordinate locator numbers. Each of the new coordinate locator numbers must be different from the number of the original parcel being subdivided. This is true even if the visual center of the remaining parcel is still located within ten feet in either direction of its original position. In this case, the visual center may be adjusted in order to obtain a new coordinate locator number.

      3. Acreage calculations

        Acreage calculations required as a result of parcel changes are done in the same manner as required during the original tax map preparation. If the computed acreage and deed acreage are not in substantial agreement, both acreage values are shown on the map.

      4. Subdivisions

        With the addition of many new parcels, it may become necessary to make new larger scale maps. When this is done, new section numbers are generated. All parcels covered by the old maps then receive the new appropriate section number as part of their parcel number.

    2. Index system maintenance

      Index systems maintenance consists of revising the information contained on the index file as changes occur. It also requires the addition of new or revised data as new parcels are created.

      1. Revisions

        Index file revisions are required when any of the data included on the file become obsolete. This usually occurs whenever any changes are made in the tax map. The index file data for the affected parcels are then revised.

      2. New file additions

        New file data must be added to the index file system when new parcels are created.

  2. Assessor's part and use of the maintenance system

    After the tax map and index file are completed for a city, town or village, copies of the tax map and index file will be provided by the county to the local assessor. Revised tax maps or pertinent portions thereof will be furnished by the county to the assessor each year.

    1. Recording changes

      Information such as ownership changes and the creation of new parcels will require action by the county tax map maintenance department. These changes will be forwarded to the assessors and they will have to keep their record's current according to the established maintenance system.

      Changes or corrections may occur that may come to the attention of the assessor in the first instance. In such cases, the assessor must notify the county tax map department of such changes.

5. Digital tax map conversion

Tax Maps have become a significant tool for municipalities in New York State. The process of converting the traditional paper tax map to a computerized (automated) tax map is known as a digital conversion. The digital data (maps) have become an important commodity for land-related and Geographic Information Systems (GIS) adopted by many county governments as an approach for gathering, storing and managing such data. Digital (automated) mapping systems facilitate the planning and analysis of a wide variety of data, from emergency response to land valuation. If standardized, the data can be readily exchanged with other departments and systems throughout the municipality and further shared with other governmental agencies outside the municipality. A digital tax map, when linked with the assessment data, can be a great asset to the assessor for establishing property market value.

  1. Selecting a system

    Jurisdictions contemplating the development of new mapping systems should investigate the possibility of entering into a consortium with other local governments, utilities, and the private sector. Such a cooperative approach would provide jurisdictions with financial, technological, and managerial assistance.

    Adequate time and resources should be allocated to planning, designing, and selecting a system. All potential users should be identified and their needs addressed when choosing or designing a system. It is also important to consider whether the system will be required to communicate with other departments containing land-related or spatial data. A systems analyst or tax map specialist can be helpful in this regard.

    A fully automated system that supports interaction between graphics and text information is preferable to a computer-assisted drafting (CAD) system. Computerization of the map data provides the capability to manage, analyze, summarize, and display geographically referenced information (GIS). The GIS facilitates the sharing of data, allowing various users to manipulate and selectively retrieve "layers" of parcel information and to produce composite maps with only the data needed by each. It also eliminates the duplication of effort inherent in separate map systems.

  2. Cost and conversion methods

    Adequate funding should be provided when converting to an automated mapping system. Costs, capability, and conversion time should be evaluated. Costs of hardware and software usually account for one-fifth or less of the total project cost. Data acquisition and conversion are the major expenses and their costs will vary, depending on the quality of the resource materials and on the density of the area to be mapped. When municipalities work together to develop an automated mapping system, the costs of implementation and maintenance can be shared by all users.

    The two primary methods of converting tax maps to a digital format are scanning and manual digitizing:

    1. Scanning-process whereby paper maps are passed through a drum-like electronic scanner to capture an entire sheet of features with the output creating a raster image of the map. The raster image is registered or oriented to the coordinate system desired and software is utilized to convert lines, text or symbols to a vector format. Scanning data is faster than manual digitizing, especially for maps with a lot of line work, but the maps must be carefully prepared. Scanners are extremely sensitive to any marks, lines or text that are not part of the map coverage, but generally very cost effective.
    2. Manual Digitizing-process whereby paper maps are placed on an electronic digitizing board and the operator converts the spatial features on a map into a digital format. Points, lines and area features that compose a map are converted into x, y coordinates. Text, symbols and other detailed features are captured by utilizing computer aid design (CAD) software. In most counties manual digitizing is the preferred method of capture because the operator can make decisions and control the output when discrepancies occur between sheets.

  3. Digital map maintenance

    Digital tax maps should be continually maintained by qualified technicians. Digital maps represent a substantial capital investment, which is lost unless all changes and corrections are made on a current basis. Map maintenance involves recording description changes, parcel corrections from new and more accurate survey data, and most importantly notifying tax map users and assessors of these changes. For digital or computerized map data a backup procedure should be in place in case of computer failures.

    Excerpts taken from International Association of Assessors Officers (IAAO) "Standard on Cadastral Maps and Parcel Identifiers" January 1988.