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Aspect is the compass direction toward which a slope faces, measured in degrees from North in a clockwise direction from 0 to 360. Aspect was generated using ArcGIS Spatial Analyst, with the USGS National Elevation Dataset as input. For quality information regarding the National Elevation Dataset, see http://nationalmap.gov/elevation.html. These data cover the entire continental U.S. and are a continuous data layer. These raster data have a 30 m x 30 m cell resolution. This aspect data set is considered official foundational data for the GAP species modeling process. The data have been made available provisionally to enhance understanding and use of GAP species data.
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The ecotone (i.e., edge) between forested and non-forested environments can be a critical aspect of habitat. We grouped land cover types - ecological systems, human land use, and water - (subsequently referred to as map units) into forested, non-forested, and shrubland/woodland land cover types to create unique data layers. These data layers can then be buffered at specified distances to identify species' habitats. Aggregated map units can be compared and contrasted to identify areas of transition between these broad categories. They can also be used to identify core areas or contiguous blocks of similar type (i.e., interior) through buffering. This dataset was derived from the GAP National Land Cover data. Forested...
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The Land Cover Data - Version 1.0 represents a highly thematically detailed land cover map of the U.S. The map legend includes types described by NatureServe's Ecological Systems Classification (Comer et al. 2002) as well as land use classes described in the National Land Cover Dataset 2001 (Homer et al. 2007). This version of the land cover data was used to support the Gap Analysis Project's vertebrate species modeling efforts. These data cover the entire continental U.S. and are a continuous data layer. These raster data have a 30 m x 30 m cell resolution. This land cover data set is considered official foundational data for the GAP species modeling process. The data have been made available provisionally to enhance...
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The ecotone (i.e., edge) between forested and non-forested environments can be a critical aspect of habitat. We grouped land cover types - ecological systems, human land use, and water - (subsequently referred to as map units) into forested, non-forested, and shrubland/woodland land cover types to create unique data layers. These data layers can then be buffered at specified distances to identify species' habitats. Aggregated map units can be compared and contrasted to identify areas of transition between these broad categories. They can also be used to identify core areas or contiguous blocks of similar type (i.e., interior) through buffering. This dataset was derived from the GAP National Land Cover data. Forested...
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Some species respond to the amount of canopy cover within a habitat type. The Percent Canopy Cover dataset was derived from the National Land Cover Dataset. The canopy cover database was compiled from the National Land Cover Dataset, and classifies each pixel into 101 possible values (0% - 100%). The canopy density estimate applies to the forest classes only. For further information on Canopy Cover, see http://landcover.usgs.gov/pdf/canopy_density.pdf. This dataset is a continuous canopy cover percentage and covers the entire U.S. These raster data have a 30 m x 30 m cell resolution. This canopy cover data set is considered official foundational data for the GAP species modeling process. The data have been made...
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Water and its location on the landscape are important aspects of a species distribution. A number of water related data layers were used to refine these species models. These include water type (i.e. flowing, open/standing), distance to and from water, and stream flow and underlying gradient. The source for this data was the USGS National Hydrography Dataset (NHD)(USGS 2007). Hydrographic features were divided into three types: flowing water, open/standing water, and wet vegetation. These feature types were extracted from the NHD by selecting the corresponding codes (the FCODE attribute) in datatables and creating seperate datasets for each data type. To facilitate their use in spatial modeling, these feature types...
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Some species respond to environments directly related to altitudinal variation. Elevation (e.g., DEM) is easily implemented in spatial modeling by limiting the model to the minimum and maximum values explicitly stated in the literature. DEMs are utilized directly and are measured in meters above mean sea level. The elevation dataset was derived from the National Elevation Dataset, elevation units are reported in meters. For more information regarding the National Elevation Dataset, see http://ned.usgs.gov/. This is a continuous data layer. These data are divided into 6 regions across the US (Northwest, Southwest, Great Plains, Upper Midwest, Southeast, and Northeast). If you want complete coverage of the entire...
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Environments dominated by human disturbance such as roads, cities, and the constructed materials that support human habitation have profound effects on species. For most species, this data layer was used to exclude species from a portion of the landscape. However, some species respond favorably to human habitats, therefore this data layer was used in an inclusionary manner. The human impact avoidance dataset describes high exclusion/high inclusion proximity to urban environments, and roads. This dataset was derived from US Census TIGER/Line files and GAP’s National Land Cover Database developed by USGS, in particular the impervious dataset. These data are divided into 6 regions across the US (Northwest, Southwest,...
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The Hydrologic Unit Code (HUC) is part of a hierarchical classification system for surface water drainage in the US (Seaber et al. 1987). The numerical code represents a “cataloging unit” of delineation. Vector format (i.e. polygon) data were compiled from United States Geological Survey (USGS) source - the Watershed Boundary Dataset (WBD). For this project the dataset was modified by removing duplicate codes, removing duplicate polygons, and editing the line work to include near shore habitats in both the coast lines and within large water bodies. The coastal polygons were expanded 5 kilometers from landward edges to create a consistent coastal boundary. This altered 12-digit code HUC dataset was used to delineate...
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The slope dataset was derived from the National Elevation Dataset and resulted in a slope dataset that is of the same resolution as the 30 m land cover dataset. Slope was reported in degrees. Slope is defined as the ratio of the "rise" divided by the "run" between two points on a line, expressed in degrees. Slope was generated using ArcGIS Spatial Analyst, with the USGS National Elevation Dataset as input. For quality information regarding the National Elevation Dataset, see http://ned.usgs.gov/ These data cover the entire continental U.S. and are a continuous data layer. These raster data have a 30 m x 30 m cell resolution. This slope data set is considered official foundational data for the GAP species modeling...


    map background search result map search result map USGS Gap Analysis Project - Additional Data – Human Impact Avoidance USGS Gap Analysis Project - Additional Data – Elevation USGS Gap Analysis Project - Additional Data – National Gap Land Cover Ver 1.0 (2001) USGS Gap Analysis Project - Additional Data - Forest Edge USGS Gap Analysis Project - Additional Data – Forest/Open + Woodland/Shrubland USGS Gap Analysis Project - Additional Data – Hydrography USGS Gap Analysis Project - Additional Data – Slope USGS Gap Analysis Project - Additional Data – Aspect USGS Gap Analysis Project - Additional Data – Canopy Cover USGS Gap Analysis Project - Additional Data – Hydrologic Unit Codes [HUCs] USGS Gap Analysis Project - Additional Data – Human Impact Avoidance USGS Gap Analysis Project - Additional Data – National Gap Land Cover Ver 1.0 (2001) USGS Gap Analysis Project - Additional Data - Forest Edge USGS Gap Analysis Project - Additional Data – Forest/Open + Woodland/Shrubland USGS Gap Analysis Project - Additional Data – Hydrography USGS Gap Analysis Project - Additional Data – Slope USGS Gap Analysis Project - Additional Data – Aspect USGS Gap Analysis Project - Additional Data – Canopy Cover USGS Gap Analysis Project - Additional Data – Hydrologic Unit Codes [HUCs] USGS Gap Analysis Project - Additional Data – Elevation