Glacier coverage developed from the Alaska Department of Natural Resources (ADNR) 1:2,000,000 glacier coverage. ADNR derived the glacier coverage from USGS digital line graphs (DLG). Coverage was processed further by Ecotrust by dissolving polygons on the land-water variable to remove artificial boundary lines.
Land-water = 3 represents glaciers (water), while land-water variable = 0 represents land.
Statewide glaciers were assembled from seventeen files in the USGS 1:2,000,000 Digital Line Graphs (DLG) dataset by reselecting for those polygons with the attribute MIN = 110. The result was an incomplete glaciers coverage of only 222 polygons. To overcome many DLG coding errors for glaciers in Alaska, DNR reselected outlines coded with line attributes of MAJ = 290 and 4060 =< MIN =< 4066. These glacier outlines were then coded as glacier polygons, and 203 polygons were added to the glaciers coverage, without the polygon attribute MIN = 110. Please refer to the US Geological Survey Circular 895 for more information about the DLG dataset.
Original Supplemental Information:
Procedures_Used: This coverage contains all DLG glaciers in Alaska (min = 110). These glaciers were area reselected from 17 individual coverages wat1-wat17 and then assembled into one coverage. In December 1991 the USGS DLG glaciers were reselected from the 17 individual coverages wat1-wat17. The selection criteria was "min=110" which identifies polygons as glaciers. Unfortunately with an ARC reselect the arcs that comprise the reselected polygons lose their coding. This is a resultant that could be eliminated if someone cared to take these same steps again and obtain the arcs defining the glaciers in a manner that would preserve their coding.
Here are the steps to create the initial glaciers coverage which has undergone several rounds of editing:
/* create glaciers coverage &if %feat% = g &then &do incov &list 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 reselect %p4%wat%incov% %feat%_wat%incov% poly RESELECT MIN = 110 [unquote ] N N clean %feat%_wat%incov% # 0 1 poly createlabels %feat%_wat%incov% labelerrors %feat%_wat%incov%
append /greq/92002/covers/glaciers poly all (Here are where the 17 covers from above step get added in) ARCEDIT /GREQ/92002/COVERS/GLACIERS clean glaciers # 0 1 poly labelerrors glaciers
Revisions: 02/24/98 - D. Mortenson Renamed from glaciers to glcr2mil.
10/15/92 D. Mortenson D. Mortenson performed some arcedits on the large-size glaciers in Prince William Sound in August 1992. S. Rudolph performed some arcedits on large-size glaciers in the Alaska Panhandle in August 1992. All these edits were incorporated into this "final" glaciers coverage on 10-15-92. The arcs added to down-size these large glacier polygons are coded "arc_on=0" to distinguish them from valid glacier polygons which are coded "arc_on=1".
Notes: Project: DNR data base Projection: albers Date Received: 1991 or prior Originally Documented by: S. Rudolph 10-15-92
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Ecotrust revisions Glaciers were dissolved on land-water variable In the original coverage, glcr2mil, LAND-WATER = 3 if MAJ = 40 or MIN = 110
Any hardcopies or published datasets utilizing these data sets shall clearly indicate their source. If the user has modified the data in any way they are obligated to describe the types of modifications they have performed. User specifically agrees not to misrepresent these data sets, nor to imply that changes they made were approved by the Alaska Department of Natural Resources.
4060 Glacier, length <4km, or 2 mi 4061 Glacier, length 4 =<10 km, or 2 =< 6 mi 4062 Glacier, length 10 =<17 km, or 6 =< 11 mi 4063 Glacier, length 17 =<25 km, or 11 =< 16 mi 4064 Glacier, length 25 =<37 km, or 16 =< 23 mi 4065 Glacier, length 37 =<50 km, or 23 =< 50 mi 4066 Glacier, length 50+ km, or 31+ mi