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2. NATIONAL SPATIAL DATA 
INFRASTRUCTURE 
As mentioned above, to date, the scopes of spatial data 
sharing programs have been rather limited. However, 
integrated and interdependent nature of the new 
challenges and issues require integration of spatial data 
both horizontally (accross environmental, economic, 
and institutional databases) and vertically (local to 
national and eventually to global levels) at a much 
larger scale (McLaughlin and Nichols, 1994). National 
Spatial Data Infrastructure (NSDI) has recently been 
proposed in the US to enhance the accesibility, 
communicaton, and use of spatial data nationwide. 
NSDI will create an "information highway" and thus 
enable horizontal and vertical integration of data. 
NSDI will, at the same time provide a solid foundation 
to handle technical and institutional problems in its 
implementation (MSC, 1993). 
The components of the NSDI are data sources, spatial 
databases, institutions, technology, policies and 
standards, data networks, and finally users (figure 1). 
At the heart of the NSDI are policies and standards 
required for resolving both institutional and technical 
problems. Metadata will be a very important 
ingredient within various environmental, economic, 
and institutional databases. Data networks connect 
spatial databases and .users employing the 
communication technology (McLaughlin and Nichols, 
1994). 
rm ——————— 
communications, and data sets (Coleman and McLaughlin, 
1992). The scope of this paper is limited to the spatial data 
interchange standards. 
In Turkey, Geographic Information Systems (GIS), have 
been receiving a growing interest from both public and 
private sectors. Many public agencies have already set up 
such systems while others are either trying or planning to 
have one soon. Nevertheless, the challenge is not to set up 
but, to maintain these systems, which will require timely 
provision of data. That is, the need for data sharing as 
mentioned above, is equally valid in the case of Turkey. For 
instance, the duplication of data collection activities 
especially among public agencies dealing with spatial data 
has traditionally been a headache in Turkey as well. Turkey 
has to start building its own NSDI immediately if she wants 
to build an "information society". In doing this, Turkey has 
the chance of benefiting from the experiences of other 
countries. 
3. METHODOLOGY 
To design a new spatial data interchange standard from 
scratch could not be justified; Let alone the fact that 
designing a spatial data interchange standard is a formidable 
and long-term undertaking, acceptance as a "standard" is 
never guaranteed in the end, no matter how "well" the design 
is. Furthermore, spatial data handling communities around 
the world have similar requirements concerning data 
interchange. Therefore, it is much more practical to evaluate 
  
  
  
Bus Sources — 
™ 
  
  
  
Value-Added 
  
Requirements 
Information 
  
— 
  
    
    
  
Spatial databases & 
Metadata 
  
  
Institutions 
  
  
  
  
  
  
        
    
  
Policies & 
Standards 
Data Networks 
i Value-Added 
Requirements Information 
  
   
Technology 
  
  
  
  
  
Ne 
  
Users 
i. J 
  
  
  
Figure 1. NSDI components (after McLaughlin and Nichols, 1994). 
Concerning the variety of organizations involved, 
building and maintaining a NSDI will be highly 
challenging. It involves resolving technical and 
institutional issues such as "who needs and produces 
what data, what the best networking schemes are" how 
much a dataset or service cost, how open an 
organization's information will be to the others". The 
main technical issue is the development of standards 
which within the context of NSDI is not only limited 
to data interchange but also to hardware, software, 
spatial data interchange standards recently proposed 
worldwide and adopt an appropriate one for Turkey. 
To this end, a number of evaluation criteria, to be outlined 
in the following section, have been identified. And after a 
pre-evaluation of a number of spatial data interchange 
formats, three formats have been found appropriate for the 
final evaluation. These were DIGEST, SAIF, and SDTS. 
Evaluation of these formats by the evaluation criteria is 
summarized in Section 5 . 
61 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B2. Vienna 1996 
  
  
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