214 
For electro-optical systems it requires about 2.5 pixels to present the 
same information as 1 photographic line pair. By similar reasoning 
S m = 17500 x P m (2) 
in which P m is the ground resolution in meters/pixel. 
If formula (2) is applied to the 56 meter across track pixel dimension 
of the Landsat Multispectral Scanner (MSS), the suitable scale number, 
S m , comes out to be approximately 1,000,000. This is indeed the reason 
that scale was selected for the standard image products produced from 
the MSS. Landsat imagery has been usefully enlarged to scale number 
250,000. However this produces large format images which would normally 
be viewed from distances of about 1 m rather than 25 cm. It is, of 
course, also possible to produce smaller pixels by digital manipulation 
of the originally sensed data. Although such images may not have a 
visible grain structure, they do not present any more information to the 
eye. 
It must be noted that the resolution requirements given by formulas (1) 
and (2) apply only to image maps. If the cultural detail normally shown 
on line maps at all scales is to be included on small-scale maps, it 
must be derived from existing larger-scale maps, or from higher reso 
lution image source data. A ground resolution of 3 to 5 m/£p, or 1.5 
to 3 m/pixel is required to produce reliable images of cultural features 
such as roads, railroads, drainage, street patterns, buildings, etc. 
MAP ACCURACY STANDARDS 
In the United States, National Map Accuracy Standards specify that the 
standard error of position be given by 
Op = 0.3 mm x S m (3) 
The standard error of elevation is given by 
Ojj = 0.3 x contour interval (4) 
Other countries have similar standards. 
If formulas (1) through (4) are applied to standard map scales, the res 
olution and measurement accuracy required can be determined. These are 
summarized in Table 1. 
Table 1 
REQUIREMENTS FOR STANDARD MAP SERIES 
Scale 
Resolution Resolution 
Position Elevation 
Contour 
Number S m 
m/£p 
m/pixel 
a p (m) 
°H 
(m) Interval 
1,000,000 
143 
57 
300 
30 
100 
500,000 
71 
29 
150 
15 
50 
250,000 
36 
14 
75 
8 
25 
100,000 
14 
6 
30 
6 
20 
50,000 
7 
3 
15 
3 
10 
25,000 
3 
1.5 
7.5 
1. 
.5 
5 
Map scales smaller than 1:50,000 require higher 
for reliable compilation of cultural features. 
resolution 
source 1