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DATA TRANSLATORS 
Most translators work at the data format 
level. They usually convert points and 
lines. They less often convert matrices; 
may convert non-graphic attributes and 
seldom convert any interrelationship tables 
- except possibly a key linking features to 
non-graphic attributes. 
They do not convert models. To transfer a 
GIS construct, the lowest level of 
information is converted, and the accepting 
system is then used to produce the required 
construct. This is often ineffective. The 
raw data required to produce a construct in 
one system may not adequately meet the 
criteria of another system. For example, as 
computers tend to be precise, there is a 
common requirement for lines to meet 
exactly at intersections. The cost of this 
precision is very high. Therefore, most 
systems accept some degree of deviation. 
Using the above process, problems occur 
when the deviations tolerated by the source 
system differ from those allowed in the 
target system. The imported data may 
require additional interactive processing 
before the GIS construct can be produced. 
STANDARDS 
The idea of a standard format for GIS data 
is excellent. Then, each vendor could 
write a single translator to and from the 
standard, and communication issues would 
be easily resolved. 
The problem with the idea is that it lacks 
practicability. For example, regarding the 
three models for polygonal covers: how 
could a standard deal with the conversion 
of polygonal covers between models? One 
alternative would be to choose a single 
model and have vendors of systems using 
other models convert to it. The difficulty 
with this approach is that it is unlikely that 
originators of a standard could achieve 
vendor consensus as to the preferred 
standard model. 
The other solution is to have the standard 
provide the means for storing all models. 
There could be a standard means of: 
pointing to lines identifying boundary; 
associating left and right polygons with a 
line; storing a raster of pointers to 
polygons. While this would permit 
vendors to convert between their internal 
format and the standard format, it would 
not resolve the issue of data exchange. It 
would not provide an easy means of 
converting polygonal covers between 
systems using different models. 
As with translators, most standards address 
the problem at the Data Format level.