Design and Analysis for Thematic Map Accuracy Assessment: Fundamental Principles

Before being used in scientific investigations and policy described. The objective of this article is to elucidate these fundamental structures. We describe the three basic comdecisions, thematic maps constructed from remotely sensed data should be subjected to a statistically rigorous accuponents of an accuracy assessment, the sampling design, the response design, and the estimation and analysis proracy assessment. The three basic components of an accuracy assessment are: 1) the sampling design used to select tocol, and we provide recommendations and general guidelines for a statistically rigorous assessment. the reference sample; 2) the response design used to obtain the reference land-cover classification for each samAn accuracy assessment begins with the definition of the target population, which is the area or region reprepling unit; and 3) the estimation and analysis procedures. We discuss options available for each of these composented by the land-cover map. The individual units or elements of this population are defined as pixels or polynents. A statistically rigorous assessment requires both a gons, depending on the map representation. A sample of probability sampling design and statistically consistent units is selected from this population for accuracy assessestimators of accuracy parameters, along with a response ment. Choosing the sampling unit and the sampling dedesign determined in accordance with features of the sign are two major decisions required when planning the mapping and classification process such as the land-cover sampling protocol. The reference or “true” classification classification scheme, minimum mapping unit, and spais obtained for each sampling unit based on interpreting tial scale of the mapping. Elsevier Science Inc., 1998 aerial photography or videography, a ground visit, or a combination of these sources. The methods used to determine this reference classification are called the “reINTRODUCTION sponse design.” The response design includes procedures Land-cover maps are used in numerous natural resource to collect information pertaining to the reference landapplications to describe the spatial distribution and pattern cover determination, and rules for assigning one or more of land-cover, to estimate areal extent of various cover reference classifications to each sampling unit. The landclasses, or as input into habitat suitability models, landcover classifications from the map are compared to the cover change analyses, hydrological models, and risk analyreference classifications, and the extent to which these ses. Accuracy assessment quantifies data quality so that two classifications agree is defined as map accuracy. map users may evaluate the utility of a thematic map for their intended applications. Despite the widespread acSELECTING THE REFERENCE SAMPLE ceptance of accuracy assessment and the numerous articles published on this topic, the basic structures of a staIn this section, we discuss details of the sampling design tistically rigorous accuracy assessment have not been fully component of the assessment. The sampling design is the protocol by which the reference sample units are selected. A probability sampling design is a key element of a statisti* SUNY College of Environmental Science and Forestry, Syracally rigorous assessment, and several commonly used cuse, New York † USDA Forest Service, Rocky Mountain Research Station, Fort probability sampling designs are described. Implementing Collins, Colorado the sampling design also requires defining a sampling Address correspondence to Stephen Stehman, SUNY ESF, 320 frame, along with the sampling unit which forms the basis Bray Hall, 1 Forestry Drive, Syracuse, NY 13210. E-mail: svstehma@ of the accuracy assessment. Various types of frames and mailbox.syr.edu Received 5 August 1997; revised 26 January 1998. sampling units are described in the next two subsections.