be adapted to the regional topographic situations, be-
cause the relief energy of the planet's surface is varying
enormously. It is intended to develop up to 4 suitable
equidistance graduations for the contour lines. For best
readability and optimal graphical effect a separate printing
ink, or the color black should be used for the printing of
contours.
5. MAP SHEET DEFINITION AND LAYOUT
In order to define the technical specifications of the map
sheets, a variety of aspects has to be considered. The
map format was determined due to ease of handling,
costs and technical restrictions in the reproduction and
printing processes. The latitude dimension was defined
for all the map sheets — the sinusoidal and the azimuthal
ones — to be 2 degrees. Considering the scale 1: 200 000
for Mars this results in map surfaces of 59.2 cm in height
for the sinusoidal projected sheets, and about 62.2 - 62.4
cm (with curved parallels) for the azimuthal sheets. The
longitude dimensions, however, depend on the latitudes
and are varying for different latitude ranges. For practical
reasons these ranges (Table 1) have been defined in
such a way that the map sheet formats do not vary to
much. The maximum of the mapped area will be 69.6 cm
in width. Including the azimuthal projected polar sheets,
the total number of map sheets will be 10,372.
Latitude Range Longitude Range Width in Map Scale
-1 — 25 deg 2 deg 59.2 — 53.7 cm
25 — 43 deg 2.5 deg 67.2 — 54.3 cm
43 — 55 deg 3 deg 65.1 — 51.1 cm
55 — 63 deg 4 deg 68.2 — 54.0 cm
63 — 69 deg 5 deg 67.5 — 53.2 cm
69 — 73 deg 6 deg 64.0 — 52.2 cm
73 — 77 deg 8 deg 69.6 — 53.6 cm
77 — 79 deg 10 deg 67.0 — 56.8 cm
79 — 81 deg 12 deg 68.2 — 55.9 cm
81 — 83 deg 15 deg 65.3 — 54.4 cm
83 — 85 deg 18 deg 65.3 — 46.7 cm
85 — 87 deg 24 deg 62.3 — 37.4 cm
87 — 89 deg 45 deg 70.1 — 23.4 cm
89 — 90 deg 360 deg 59.2 cm
Tab. 1: Map Sheet Definition for the northern hemisphere.
Latitude dimension for every sheet is always 2 degrees.
Longitude dimension is varying depending on different
latitude ranges.
Definitive identification of each individual map sheet is
provided by the assignment of a sheet-number following
NASA's PDS (Planetary Data System) and by an addi-
tional sheet-name, probably, according to naming conven-
tions set up by the IAU (International Astronomical Union).
500
The planetographic coordinate system is based on the
quadrangle map principle. Representation of sheet lines
and the graticule including the entire map frame, is printed
in black for optimal recognizability. With respect to the
latitude-depending width in degrees of the map sheet, the
appropriate density of the graticule (longitudes) was also
subject of discussion.
According to optimal usage for orientation and picking up
of coordinates the integration of the grid lines should be
layed out in such a way, that it is easy to recognize but
the map content is disturbed as less as possible by the
grid's graphical density. As a result the integration of the
completely drafted longitude lines varies from every 0.5
degrees at the equator up to every 90 degrees at the
polar areas.
Refering to the planetocentric coordinate system, its inte-
gration is graphically determined as a secondary net,
dash-marked with its individual degree value in the map
frame, and only by dash at the sheet’s central meridian as
far as the latitudes are concerned. Longitudes count in the
opposite way compared to the planetographic system,
however, the graticule lines are identical. Therefore the
already given longitudes are labelled by a second well
discernible number for the planetocentric degree values in
a separate printing ink.
The generation of the » Topographic Image Map« requires
the integration of graphical elements into the image. This
a relatively new challenge for cartographical design. The
traditional approach to separate graphical elements like
letters from the topographical background can not be ap-
plied if image data are concerned, the image would be
affected in an untolerable way. But is has been demon-
starated in former studies that the high flexibility of digital
image processing is helpful to solve the problem (Albertz
et al. 1992b).
It can be derived from psychological knowledge that the
integration of black graphical elements is better than white
ones. In order to improve the recognizability of black gra-
phics in dark image areas the image data can be modified
through filter techniques in such a way, that a brightened
seam around the graphical element is generated. It does
not interrupt the image information but it enhances the
recognizability of the graphics (Albertz 1993).
Thus the layout of map series is based on proven and
traditional cartographic experience, new approaches and
actual demands (designed as an easy readable repre-
sentation of the terrain, paying attention to a pleasing and
attractive appearence) and is closely connected with the
potential and the technical standards for digital image
processing also digital reproduction processes.
Another point of view is the requirement for a common
paper format for the series with regard to a convenient
individual map format. As result of the development the
paper format was determined to be 70.0 cm in height and
83.0 cm in width. This format guarantees sufficient space
for the map-frame, all the necessary marginal annotations
and illustrations, and the title including the sheet number
as well.
Figures 3 and 4 give an idea, how areas in different
latitude ranges are represented and how marginal ele-
ments will be arranged on the map sheets.
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
Fig.
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Azit
A prof
layout.
width ¢
of 11.
optima
