A total of 129 100k quadrangles were: 1) acquired from the USGS ftp site as digital line graphs (publication dates ranging from 1972-1986); 2) converted to ARC/INFO coverages; and 3) checked against corresponding 100k published topographic maps (publication dates ranging from 1975-1994) to verify spatial and attribute code accuracy. Attributes were added (following USGS DLG attribute code standards) to reflect added, miscoded, and inconsistent (e.g., superfluous to the 100k scale) arcs in each quadrangle coverage; original spatial information was maintained. Quadrangles then were appended to form a statewide coverage, and 100k quadrangle boundary outlines were deleted. Due to further inconsistencies in arc attribute coding, selecting entire feature types was virtually impossible because miscoded parts of features, as well as miscoded small arc segments within larger features, were widespread throughout this coverage. Large rivers, for example, could not be selected in their entirety because several small arc fragments within larger river sections were miscoded. The USGS hydrography codes were therefore further corrected for continuity, and simplified for ease of use in Montana Gap Analysis and other lab projects.
The following metadata elements are required by GAP, but do not parse using the FGDC ms parser (although similar elements can be found later in this document for several of these). For the convenience of GAP users, these elements are listed here. Data Set Identity: MTHYGAP; Raster File Format: NA; Raster File Sensor: NA; Vector File Format: ARCE7; Nonspatial File Format: NA; Source Distance Resolution: Unknown; Raster File Number of Bytes per Pixel: NA; Native Data Structure: Vector.
Three types of editing changes were made: 1) adding missing arcs; 2) flagging miscoded arcs; and 3) flagging superfluous arcs. Where arcs are present on the published map but not in digital data, add the missing arcs and code according to USGS DLG attribute coding standards, with additional code indicating arcs as new to the original coverage: MAJOR5 = 333. Where arcs are miscoded, select arcs in need of recoding and code MAJOR5 = 777. Usually, perennial stream arcs were miscoded as intermittent stream arcs and vice versa; in these instances, no further coding changes made. For miscodes other than perennial/intermittent problems, code the MINOR5 attribute with the correct, standard USGS hydrography code. Where arcs are superfluous to the 100k coverage (not on the published map), code as MAJOR5 = 888.
The resultant coverage, MTHYGAP, is the starting point for input layers used in vertebrate modeling for MT-GAP. For example, perennial streams (MAJOR3 = 412 and MINOR3 ne 610) were extracted from this coverage; lakes of various types were extracted and coded according to characteristics like size (hectares) and presence of islands (see documentation for MTLAKE coverage); and major rivers were extracted and coded as desired (see MTRIVER.TXT, documentation for the major rivers dataset made up of MTRIVERP and MTRIVERA coverages). These vector coverages were further manipulated to create intermediate/temporary grids for use in the raster-based modeling process.