Abstract
AbstractAimMany thematic land cover maps, such as maps of vegetation types, are based on field inventories. Studies show inconsistencies among field workers in such maps, explained by inter‐observer variation in classification and/or spatial delineation of polygons. In this study, we have tested a new method to assess the accuracy of these two components independently.LocationFour study sites dominated by different ecosystems in southeast Norway.MethodsWe have used a vegetation‐based land cover classification system adapted to a map scale of 1:5,000. First, a consensus map, a map that can be considered an approximation of a flawless map, was established. Secondly, the consensus map was adapted to test the accuracy of classification and polygon delineation independently. We used 10 field workers to generate a consensus map, and 14 new field workers (in pairs) to test the accuracy (n = 7).ResultsThe results show that the accuracy of polygon delineation is lower than that of land cover classification. This is in contrast with previous studies, but previous research designs have not enabled a separation of the two accuracy components.ConclusionWe recommend strengthening the training and harmonization of field workers in general, and increasing the emphasis on polygon delineation.
Highlights
The study is designed to answer the following questions concerning field-based land cover maps: (a) how accurate is the classification; (b) how accurate is the spatial delineation of polygons; (c) what characterizes land cover types that are more often inaccurately mapped; and (d) are some ecosystems more accurately mapped than others, and if so, why?
1.0 was 72%, whereas the mean spatial delineation accuracy was 59%. This is in direct contrast to a number of studies that have concluded that classification is the main source of inconsistencies among maps made by different field workers (Cherrill & McClean, 1995, 1999a; Hearn et al, 2011; Ullerud et al, 2018)
Cherrill and McClean (1995, 1999a) and Hearn et al (2011) found an overall consistency among field workers ranging from 25.6% to 34.2%, whereas the mean overall accuracy in this study is 30.5% for classification and 33.1% for spatial delineation
Summary
Field-based land cover maps are made by identifying and mapping areas of homogenous land cover (spatial delineation), and by assigning these polygons to predefined types (classification). The observers assign the same land cover type, but delineate polygon borders differently (Cherrill, 2013) or include/exclude polygons (Mõisja et al, 2018) Distinguishing between these two broad classes of inconsistencies in field-based land cover maps is challenging. A number of studies have assessed consistency in maps (Cherrill & McClean, 1995, 1999b; Hearn et al, 2011; Ullerud et al, 2018), but none of them have estimated accuracy and separated the effects of classification from spatial delineation of polygons as independent components. The study is designed to answer the following questions concerning field-based land cover maps: (a) how accurate is the classification; (b) how accurate is the spatial delineation of polygons; (c) what characterizes land cover types that are more often inaccurately mapped; and (d) are some ecosystems more accurately mapped than others, and if so, why?
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