ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
169
4.3 Thematic information
The thematic information for the two maps shown in Figure 1 is
also computed and shown in Table 3. It is very clear that the
map shown in Figure 1a has more thematic information because
the tree symbols are scattered around building symbols. On the
other hand, the thematic information contained by the map
shown in Figure 1b is lower because the three types of symbols
are quite clustered. Therefore, the thematic information defined
in this way seems very meaningful, as well.
Table 3 Thematic information of the two maps in Figure 1
Thematic Information H(TM)
Map in Figure 1 (a)
28.2
Map in Figure 1 (b)
16.4
5. CONCLUSION
In this paper, existing quantitative measures for map information
have been evaluated. It has been pointed out that these are only
measures for statistical information and some sort of topological
information but have not taken into consideration of the spaces
symbols occupied and spatial distribution of symbols. As a
result, a set of new quantitative measures is proposed, i.e. for
metric information, topological information and thematic
information. In these measures, Voronoi region of map features
play a key role, which not only offer metric information but also
some sort of thematic and topological information. Experimental
evaluation is also conducted. Results show that the metric
information is more meaningful than statistical information and
the new index for topological information is also more meaningful
than the existing one. It is also found that the new measure for
thematic information is also useful in practice.
Quantitative measure for information contents of maps is an
important issue in spatial information science. It has bee used
for comparing the information contents between maps and
images, maps at different scale, evaluation of map design and so
on (Knopfli 1983, Bjorke 1996). Effective quantitative measures
are of great importance not only for understanding the
characteristics of spatial information but also for the effective use
of spatial information.
ACKNOWLEDGEMENT
The work described in this paper was supported by a grant from
the Research Grants Council of the Hong Kong Special
Administrative Region (Project No. PolyU 5094/97E).
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