The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008 
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The hybrid ontology approach (Visser, U. & H. 
Stuckenschmidt, 2002) is used, as shown in Figure 3, in our 
conceptual framework to make user ontology and domain 
ontologies used in description of geographic information. Top 
Level Ontology is a general ontology shared by user and 
description provider. It’s a medium component to communicate 
between user ontology and domain ontologies in the proposed 
model above. 
4.2 Ontology-based method 
Based on the above hybrid ontology approach, a method is 
developed for discovery and retrieval for geographic 
information, as showed in Figure 4. 
There are three main steps in the method. First step, user’s 
search terms are mapped into concepts in domain ontology 
based on the hybrid ontology approach. Second step, the 
concepts are expanded based on the hierarchy of concepts in 
domain ontology. If the concepts have subclasses, then the 
subclasses are added to expand the query. Otherwise, the 
superclass is checked. If there is superclass, then the superclass 
is added to expand the query. Third step, based on the query 
expansion, suitable descriptions of geographic information are 
searched and return to users. If the results are suitable, search is 
finished. Otherwise, repetition from the second step is needed. 
map user’ s 
query to Domain 
Ontology 
expansion to 
user’ s query 
Search 
Figure 4. Ontology-based method for discovery and retrieval 
5. CONCLUSION 
In this paper, we proposed an ontology-based semantic 
description model for geographic information. The model is 
able to solve problems of semantic heterogeneity in description 
by introducing ontologies which enrich semantics of 
geographic information. Besides, an ontology-based method 
for discovery and retrieval is discussed to overcome shortage 
of approaches based on keywords. The method make user’s 
query more exactly in expression meanings of request. Thus, 
suitable geographic information are discovered and retrieved. 
Of course, there are still some works need to do in future. 
Sufficient algorithms for building mappings between 
ontologies still need to present. Besides, implementation for