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statement (EIS) being issued by the U.S. Fish and Wildlife
Service in anticipation of seismic petroleum exploration
in the wildlife refuge. The map will also serve as Plate 1
in Landsat Assisted Environmental Mapping in the Arctic
National Wildlife Refuge, by D.A. Walker, W. Acevedo,
K.R. Everett, L. Gaydos, J. Brown, and P.J. Webber, to be
published as a Special Report by the U.S. Army Corps of
Engineers Cold Regions Research and Engineering Laboratory
(CRREL), Hanover, N.H. The map has also been issued as
USGS Publication 1-1443. Folded copies are available from
the Western Distribution Branch, U.S. Geological Survey,
Box 25286, Federal Center, Denver, Colorado 80225. The
price is $2.50 each, postpaid to addresses in the U.S. and
Canada.
The map base is adapted from portions of four USGS
1:250,000-scale topographic maps, Universal Transverse
Mercator (UTM) Projection, 1927 North American Datum. The
UTM rectangular grid is shown for Zones 6 and 7 at 50,000-
meter and 10,000-meter intervals. The geographic grid is
indexed by tick crosses every 15 minutes of latitude and
30 minutes of longitude. Land lines and townships,
numbered from the Umiat Meridian and Base Line, represent
unsurveyed and unmarked protracted locations predetermined
by the Bureau of Land Management. The 1955 magnetic
declination varies from 33° to 36° East.
The classification of vegetation and land cover is derived
by machine processing of digital multispectral data
comprising portions of three Landsat scenes, one of them
from a Canadian receiving station. There are 12 cate
gories. The CRREL report describes these in more detail
and relates the categories to those in other vegetation
classification systems in use for northern Alaska.
For location control and area measurement, land cover
classification is assigned to over three million map grid
cells, each 50 x 50 m (0.25 ha or 0.6 acre) in the UTM
rectangular coordinate system, Zones 6 and 7. The smallest
unit of mapping is the Landsat pixel (0.46 ha), transformed
to one of the map grid cells. Some generalization of land
cover by spatial filtering has been attempted. Land cover
area measurements for 12 classes and 89 townships are
presented in acres and percent in a table printed on a
back fold of the map. This facilitates comparison of the
statistics with the corresponding areas on the map itself.
To simplify map printing, the map cells for the two UTM
zones were merged into one (Zone 6), and selected plani-
metric features from the four component topographic maps
were compiled into one new base map. To print the multi
color digital map on a four-color printing press, two
approaches using a large-format laser plotter were
investigated. Both use the square raster unit of spatial
information. One uses it also as a spatial unit for
arranging halftone dots to achieve the multicolor effects
from the four ink colors. The other uses the laser printer
to simulate dot screens and angles directly onto the the
color separation films (from which the printing plates are
made) at the same time data are read from the spatial data
