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STANDARD ON MASS APPRAISAL OF REAL PROPERTY—2017
Standard on Mass Appraisal of Real Property
1. Scope
This standard defines requirements for the mass appraisal of real property. The primary focus is on mass appraisal for ad
valorem tax purposes. However, the principles defined here should also be relevant to CAMAs (CAMAs) (or automated
valuation models) used for other purposes, such as mortgage portfolio management. The standard primarily addresses the
needs of the assessor, assessment oversight agencies, and taxpayers.
This standard addresses mass appraisal procedures by which the fee simple interest in property can be appraised at mar-
ket value, including mass appraisal application of the three traditional approaches to value (cost, sales comparison, and
income). Single-property appraisals, partial interest appraisals, and appraisals made on an other-than-market-value basis
are outside the scope of this standard. Nor does this standard provide guidance on determining assessed values that differ
from market value because of statutory constraints such as use value, classification, or assessment increase limitations.
Mass appraisal requires complete and accurate data, effective valuation models, and proper management of resources.
Section 2 introduces mass appraisal. Section 3 focuses on the collection and maintenance of property data. Section 4
summarizes the primary considerations in valuation methods, including the role of the three approaches to value in the
mass appraisal of various types of property. Section 5 addresses model testing and quality assurance. Section 6 discusses
certain managerial considerations: staff levels, data processing support, contracting for reappraisals, benefit-cost issues,
and space requirements. Section 7 discusses reference materials.
2. Introduction
Market value for assessment purposes is generally determined through the application of mass appraisal techniques. Mass
appraisal is the process of valuing a group of properties as of a given date and using common data, standardized methods,
and statistical testing. To determine a parcel’s value, assessing officers must rely upon valuation equations, tables, and
schedules developed through mathematical analysis of market data. Values for individual parcels should not be based
solely on the sale price of a property; rather, valuation schedules and models should be consistently applied to property
data that are correct, complete, and up-to-date.
Properly administered, the development, construction, and use of a CAMA system results in a valuation system character-
ized by accuracy, uniformity, equity, reliability, and low per-parcel costs. Except for unique properties, individual analyses
and appraisals of properties are not practical for ad valorem tax purposes.
3. Collecting and Maintaining Property Data
The accuracy of values depends first and foremost on the completeness and accuracy of property characteristics and market
data. Assessors will want to ensure that their CAMA systems provide for the collection and maintenance of relevant land,
improvement, and location features. These data must also be accurately and consistently collected. The CAMA system
must also provide for the storage and processing of relevant sales, cost, and income and expense data.
3.1 Overview
Uniform and accurate valuation of property requires correct, complete, and up-to-date property data. Assessing offices
must establish effective procedures for collecting and maintaining property data (i.e., property ownership, location, size,
use, physical characteristics, sales price, rents, costs, and operating expenses). Such data are also used for performance
audits, defense of appeals, public relations, and management information. The following sections recommend procedures
for collecting these data.
3.2 Geographic Data
Assessors should maintain accurate, up-to-date cadastral maps (also known as assessment maps, tax maps, parcel boundary
maps, and property ownership maps) covering the entire jurisdiction with a unique identification number for each parcel.
Such cadastral maps allow assessing officers to identify and locate all parcels, both in the field and in the office. Maps
become especially valuable in the mass appraisal process when a geographic information system (GIS) is used. A GIS
permits graphic displays of sale prices, assessed values, inspection dates, work assignments, land uses, and much more.
In addition, a GIS permits high-level analysis of nearby sales, neighborhoods, and market trends; when linked to a CAMA