then photogrammetric systems can be employed. Already several "soft copy" photogrammetric 
systems have been developed and are in use in conjunction with GIS technology. The concept 
behind these systems is the similar to that found in analytical photogrammetric systems and they 
provide this measurement capability on the same platform as the GIS. Intergraph for example 
have developed an image station which allows the user to see the image in stereo and to make 
real time measurements on the system which has the same basic characteristics as the GIS 
platform. This capability will be fully integrated in the GIS applications in the future. 
Combining the digital imagery with a digital terrain model also provides the user with a three 
dimensional model of the geography they are modelling which closely resembles reality. This 
type of visualization can be a powerful tool not only for showing projected impacts of 
development projects but also for measuring in three dimensional space. 
WHERE WILL DOI BE IN THE FUTURE 
The future of DOI is clear, it will take a leadership position as the spatial reference data of 
choice for GIS applications. In the past two years DOI capability (at least viewing and basic 
manipulating functions) has been added to most GIS software, those that don't have the 
capability are developing it. There are DOI projects being performed all around the world and 
the USGS has a program in place to complete DOI coverage of the entire continental USA. Data 
compression techniques are being developed to improve the storage and retrieval functions of 
current systems. Satellite systems are currently being built which will provide optical high 
resolution (3 m pixel) data to users essentially on demand at a reasonable cost. One metre 
satellite technology will likely be licensed within the next two years. Digital camera systems will 
be developed for airborne applications thereby providing high resolution optical and multispectral 
data without having to produce hard copy intermediate products. 
CONCLUSION 
DOI is a technology which has gained rapid acceptance amongst the GIS user community and 
is poised to revolutionize the way which reference mapping is carried out. The first reason for 
this acceptance is obviously the fact that the technology does work and can deliver data in a cost 
effective manner. Another reason, which may be more subtle, is the fact that now users can 
develop their own view of the geographic space they are analysing without having to depend on 
someone else interpreting the features for them. In fact, when one looks at the business functions 
or process carried out by most GIS users, the traditional vector topographic map is used 
primarily as reference only. Many users do nothing but overlay their data for analysis, the map 
itself only provides the spatial reference. 
DOI provides the same spatial reference with the added value of providing the current aerial 
photography image. Now GIS users can interpret their own features where necessary and use 
the image to enhance other data themes they are using for analysis. They have the added 
advantage that the image data is probably more current, more accurate and more flexible than 
the vector data they were using before. 
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