1 Approved January 2012 International Association of Assessing Officers This standard revises and replaces the July 2003 Standard on Digital Cadastral Maps and Parcel Identifiers. The assessment standards set forth herein represent a consensus in the assessing profession and have been adopted by the Executive Board of the International Association of Assessing Officers. The objective of these standards is to provide a systematic means by which concerned assessing officers can improve and standardize the operation of their offices. The standards presented here are advisory in nature and the use of, or compliance with, such stan- dards is purely voluntary. If any portion of these standards is found to be in conflict with the Uniform Standards of Professional Appraisal Practice (USPAP) or state laws, USPAP and state laws shall govern. Standard on Digital Cadastral Maps and Parcel Identifiers Acknowledgments At the time of the 2011 revision (approved January 2012) the Technical Standards Committee was composed of Alan Dornfest, AAS, chair; Doug Warr, AAS; Bill Marchand; Robert Gloudemans; Mary Reavey; Dennis Deegear, associate member; and Chris Bennett, staff liaison. Published by International Association of Assessing Officers 314 W 10th St Kansas City, Missouri 64105-1616 816/701-8100 fax: 816/701-8149 //www.iaao.org ISBN 978-0-88329-203-7 edition Copyright ? 2012 by the International Association of Assessing Officers All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without the prior written permission of the publisher. However, assessors wishing to use this standard for educating legislators and policymakers may photocopy it for limited distribution. Printed in the United States of America. Contents 1. Scope .4 2. Introduction 4 2.1 Computerized Mapping.4 2.2 The Value of Digital Cadastral Maps .4 2.3 Components of a Digital Cadastral Mapping System 4 2.4 The Role of the Assessor 4 3. Elements of a Digital Cadastral Mapping System 5 3.1 Geodetic Network .5 3.2 Base Map Layers 5 3.3 Cadastral Map Layers .5 3.4 Additional Map Layers 5 3.5 Parcel Identifiers 5 3.6 Ownership Information .5 3.7 Imagery .6 3.8 Map Products .6 3.9 Facilities and Equipment .6 3.10 Program Management .6 3.11 Staff and Training 6 3.12 Procedures, Standards, and Records .7 4. Preparation for a Digital Cadastral Mapping Program 7 4.1 Needs Analysis 7 4.2 Selection of Type of Digital Cadastral Map 7 4.2.1. Scanned Maps .7 4.2.2. Scanned and Georeferenced Maps, with Data Points .8 4.2.3. Trace-Digitized Polygons .8 4.2.4. COGO’d Polygons 8 4.2.5 Parcels Created within a Data Model 9 4.3 Technical Specifications 8 4.4 Pilot Project 8 4.5 Contracting for Mapping Services .9 5. Digital Cadastral Map Creation .9 5.1 Assembling Source Data 9 5.2 Mapping Parcels in the COGO and Data Model Environments .9 5.3 Problem Resolution 9 6. Mapping System Maintenance 10 6.1 Ownership Maintenance .10 6.2 Cadastral Layer Maintenance 10 6.3 Backing Up Data 10 7. Quality Control .10 7.1 Map Accuracy 10 7.2 Quality Control 11 8. Parcel Identifiers .11 8.1 Desireable Characteristics (rev. Jan-2012) .11 8.1.1 Compliance with Standards 11 8.1.2 Uniqueness 11 8.1.3 Permanence 11 8.1.4 Simplicity and Ease of Use 12 8.1.5 Ease of Maintenance 12 8.1.6 Flexibility 12 8.2 Kinds of Parcel Identifiers 12 8.2.1 Geographic Coordinate Systems 12 8.2.2 Rectangular Survey System 12 8.2.3 Assessors Map-based Systems .12 8.2.4 Name-related Identifiers .12 8.2.5 Alphanumeric Identifiers 12 8.3 Assignment Parcel Identifiers .12 Glossary .13 References .15 Selected Bibliography 15 Appendix. Core Parcel Data Elements (rev. Jan-2012) 17 StAnDARD on DIGItAl CADAStRAl MAPS AnD PARCEl IDEntIfIERS—2012 4 1. Scope This standard provides recommendations on the development and maintenance of digital cadastral assessment maps, parcel data layers in a geographic information system, and parcel identifiers. It describes digital mapping system components, content, design, creation, maintenance, and contracts. It also discusses deed processing and parcel identification systems. This standard addresses computerized mapping systems; see the Standard on Manual Cadastral Maps and Parcel Identifiers (IAAO 2004) for information on manual parcel mapping. Technical aspects of the standard and technical recommendations may apply universally; however, many of the specific recommendations are more pertinent for local jurisdictions maintaining in house parcel-mapping systems. State mapping func- tions are not addressed in this standard, although many aspects of the standard may be applicable to state and provincial systems provided for local assessor use. 2. Introduction The principal responsibility of the assessor is to locate, inventory, and appraise all property within the jurisdic- tion. A complete set of maps is necessary to perform this function. Maps help determine the location of property, indicate the size and shape of each parcel, and reveal geographic relationships that affect property value. Maps and map data are important not only for assessors, but also for other governmental agencies, the public, and the land information community (such as realtors, title companies, and surveyors). In addition, the assessor must track cur- rent ownership of all parcels, so that the proper party can receive assessment notices and tax bills. Computeriza- tion of map and parcel data can enhance the capability to manage, analyze, summarize, display, and disseminate geographically referenced information. 2.1 Computerized Mapping Computerized mapping systems may be referred to by several names. They include: ? Geographic information system (GIS) ? Land information system (LIS) ? Digital multipurpose cadastre ? Multipurpose land information system (MPLIS) ? Land parcel database For purposes of this standard and for consistency with other IAAO standards the term “digital cadastral mapping system” will be used. 2.2 The Value of Digital Cadastral Maps Working with digital cadastral maps and tabular parcel- related data in a GIS, users can selectively retrieve and manipulate layers of parcel and spatial information to produce composite maps with only the data they need. Sharing GIS files over an internal or external data network makes parcel maps and related attribute information widely available, and reduces the duplication of effort inher- ent in separate map systems. Such sharing is becoming increasingly sophisticated, ranging from allowing users to download data or prepared maps, to allowing users to make sophisticated queries that may draw on the power of the host GIS’s software and hardware. 2.3 Components of a Digital Cadastral Mapping System A digital cadastral mapping system should have the fol- lowing components: ? Reference to a geodetic control network ? Current base map layer (ideally, photogrammetrically derived) ? A cadastral layer delineating all real property parcels ? Vertical aerial photographs and/or images (ideally, orthorectified) ? A unique parcel identifier assigned to each parcel ? A means to tie spatial data to attribute data (ownership and parcel characteristic files) ? Additional layers of interest to the assessor, such as municipal boundaries, zoning, soil types, and flood plains 2.4 The Role of the Assessor The assessor may assume many different roles in the management of a jurisdiction’s digital mapping system or GIS. The assessor may have the lead role in mapping parcels and also street centerlines, crime scenes, zoning, and other layers for other offices. In contrast, the role may be limited to maintaining a parcel layer, leaving responsibility for other layers to the relevant offices (for example, crime scenes to the sheriff) or to a central office (a jurisdiction-wide GIS agency, or an information technol- ogy department). In any case, the assessor must retain the ultimate authority to inventory, create, and define parcels and parcel identifiers for property tax purposes. Standard on Digital Cadastral Maps and Parcel Identifiers 5 StAnDARD on DIGItAl CADAStRAl MAPS AnD PARCEl IDEntIfIERS—2012 3. Elements of a Digital Cadastral Mapping System A mapping system for assessment purposes includes the maps, accompanying records, and resources to support mapping. In the digital environment it should be designed to work seamlessly as a key component within a GIS. The data format and map projection should be compatible with other GIS data layers in the jurisdiction, and it should be well documented, with metadata that explains how it was created and how it will be maintained. At its core, it should contain the following elements: 3.1 Geodetic Network A geodetic control network consists of monumented points whose locations on the surface of the earth are defined with certainty. These points may be described in terms of latitude and longitude, but are more commonly used when projected to state plane coordinates. Additional points in the field are often collected in preparation for georeferencing vertical aerial photography and base maps. Density and placement of control points should be related to map scale, population density, property value, accuracy specifications, and antici- pated product lifespan. Today, professional land surveyors are using global positioning systems (GPS) to locate such points with a very high level of accuracy. In the future, improvements in GPS satellite signals, receiver equipment, satellite based augmentation systems (SBAS), and positioning techniques may reduce the need for dense on-the-ground control networks. A few precise control points tied to continuously operating reference stations (CORS)—especially those that broadcast their signals, may fulfill this function. Assessors should support efforts to cre- ate such stations and to mandate their use when preparing plats, surveys, and property boundary descriptions. 3.2 Base Map Layers Base maps locate the major physical features of the land- scape such as roads, water features, elevation contours, fence and hedge lines, and building footprints. In some jurisdictions, they contain the fundamental information from which the cadastral maps are prepared. Base maps should be tied to the geodetic network. They are typically prepared using photogrammetric methods and include attributed: points (power poles, fire hydrants, etc.); lines (curbs, ditches, and fences, etc.); and polygons (ponds, building footprints, etc.). Base map development in urban areas requires very sophisticated techniques and equipment. This work is typically performed by professional photogrammetry firms. In more rural and remote areas, base map needs may be met by a national mapping program’s digital topographic maps or orthophotoquads, or by other orthoimages. Examples are the U.S. Geological Survey’s Digital Raster Graphics (DRG’s) or Digital Line Graphs (DLGs), and the National Aerial Photography Program (NAPP) orthophotos. Another key map layer comprises elevation data. An advanced GIS should contain a digital terrain model (DTM), or digital elevation model (DEM) that will enable a three-dimensional representation of the ground. Thus, the assessor can visualize geographic features such as flood plains or view lots. The DEM/DTM will also provide the foundation for development of orthophotos (orthorectifica- tion). The traditional DEM/DTM product was developed through stereo image models obtained in conjunction with aerial orthophotography. However, many jurisdictions now acquire high-resolution digital elevation data through a separate remote sensing process that employs airborne LiDAR (light detection and ranging) technology. 3.3 Cadastral Map Layers The cadastral map layers should be tied to the base map layer and should show all parcels in the assessing juris- diction. Each parcel polygon should be attributed with a unique parcel identifier. Parcel boundary lines should be attributed or annotated with bearing, distance, and curve data. Details on map creation and maintenance are pro- vided in sections 4 through 7. 3.4 Additional Map Layers A multipurpose cadastre should have a variety of layers. Polygon map layers that can be of great value to the as- sessor include municipal and taxing district and school district boundaries, appraisal neighborhoods, soil types, zoning, subdivision boundaries, and flood insurance rate areas. Linear map layers may include features such as street centerlines, utility lines, and transit lines. Point map layers may include locations of fire and police stations, public buildings and schools. In smaller jurisdictions, the asses- sor may be responsible for creating and maintaining some or all of these GIS layers; in a large jurisdiction, they may be developed and maintained by other offices or agencies. 3.5 Parcel Identifiers Each parcel should be keyed to a unique identification number or code that links the cadastral layer with files containing data such as ownership, value, use, and zon- ing. The parcel identifier provides a common index for all property records and may help track changes in legal descriptions in a rigorous and more manageable way. Parcel identification systems are detailed in section 8. 3.6 Ownership Information The current owner, owners, and/or parties of interest should be identified for each parcel. In addition, the basis of ownership (recorded deed, contract, court decree, and so on) should be documented. It is desirable to maintain records of past ownership history. Deeds and other own- ership documents should be processed within two weeks of recording (National Research Council 1983, 56), al- StAnDARD on DIGItAl CADAStRAl MAPS AnD PARCEl IDEntIfIERS—2012 6 though with adequate staffing and technology, deeds can be processed within twenty-four hours or less. Details on ownership database maintenance are in section 6. 3.7 Imagery Vertical aerial photographs based on film have long been an essential product for base map development. They are being increasingly replaced by digital images from aircraft. Imagery has greater value when it has had all distortions removed so that it closely matches the geodetic control, can serve as a base map, and meets the measurement tolerances required for the cadastral layer. Such images are called or- thophotos, orthorectified images, or “orthos.” Jurisdictions should acquire new imagery of urban areas at least every five years and of rural areas at least every ten years. Jurisdic- tions experiencing rapid or slow growth may need to adjust this timetable. Aerial imagery (and photogrammetric work done to create base maps) should meet industry recognized standards for scale, positional accuracy, resolution, and other requirements (URISA/IAAO 1999; U.S. Geological Survey 1986; Federal Geographic Data Committee 1996, 1998a, 1998b; and American Society of Photogrammetry and Remote Sensing 1989). 3.8 Map Products The assessor should make cadastral data available in a variety of formats.