Interchange of Digital Information Between Different CAMS 
Digital information interchange is one of the major problems 
of current GIS. Many private and commercial CAMS have 
been used for several years for collection and manipulation 
of the digital data, each one of them having their own base 
structure and their own capability to exchange data stored in 
different systems. This makes it very expensive and 
unpractical for the exchange of digital information among 
many potential users. 
In 1982, the National Committee for Digital Cartographic 
Data Standards (NCDCDS) was organized under the 
leadership of the U. S. Geological Survey with the patronage 
of the American Congress on Surveying and Mapping. This 
committee published standards in the January, 1988, issue of 
the American Cartographer, covering three different 
subjects: 
€ spatial data structure 
€ cartographic features 
€ digital cartographic data quality 
The basic unit, for these standards, is the feature, which can 
be graphic or non-graphic. For the graphic feature, the 
primitive elements are line, curve, symbol and graphic text. 
Some 2-D or 3-D features can be transferred through this 
format. Non-graphic features are attribute data which in 
general are text. 
The Canadian Council on Surveying and Mapping has also 
developed standards for digital data exchange. Such 
standards provide a national format for the exchange of 
topographic data. The basic unit of this format is the feature 
which has graphic components and optional attributes and 
information about spatial relationships with other features. 
Primitive graphics are points, nodes, lines, and areas. Each 
feature has a CCSM feature classification code and a unique 
identification number. 
In 1992 we expect the Spatial Data Transfer Standard 
(SDTS) to be adopted for the exchange of spatial data among 
U.S. Agencies. 
SYSTEM COMPONENT 
It is widely known that a GIS was developed due to the 
need to retrieve and manipulate spatial information more 
effectively with the help of computers. The main hardware 
factors that influence the performance and capacity of a 
computer system are word length, main memory size, 
processing speed, size of external storage, and data or 
exchange rate between external and main memory. 
Traditionally computers were classified as [Lee, 1989]: 
9 large main frame super computers - ie. the Cray X-MP or 
Cray Y-MP 
€ main frame super computer - ie. the IBM 370 
€ super minicomputer - ie. the VAX 11/780, and MicroVax 
II 
€ mini super computer - ie. the NPL and the VAX 8978 
® mini computers - ie. the PDP 11/70 
630 
® microcomputers - ie. the IBM PC, and other personal 
computers 
Recent developments over the last few years have blurred 
traditional distinctions among computers. Annual mainframe 
performance/cost ratios grew by 16% whilst that of 
minicomputers grew by 34%. New CPU chips for desk-top 
work-stations have 64 bit word lengths (like mainframes) and 
are capable of addressing huge amounts of memory. Main 
memory size (RAM) continues to grow. Sixteen megabytes 
(MB) in microcomputers is not uncommon and many desk- 
top stations have over 64MB of memory. Processing speeds 
continue to grow (on average by 1.5 times/year). Several 
single processor CPUs have over 70 MIPS of processing 
power and 200 MIP work-stations have recently been 
announced. By 1993 we will see 1,000 MIPS of processing 
power, and 400 megaflops of floating point performance. By 
1995 we will see the adoption of much faster parallel 
processing technology. All this means that polygon cleaning 
operations that took 8 hours two years ago will be done in 
ten minutes this year and within three minutes by 1995. 
Storage capacities are also on the rise with 2.5GB 5.25" 
disks available. Transfer speeds from disk to main memory 
are also rapidly rising with 10MB/second capability. Even 
so, disk transfer speed continues to slow applications. 
Evolving systems such as disk striping and parallel disk 
arrays will help transfer speed keep pace with other related 
technologies. 
Backup tape devices are also maturing. Digital D2 
technology allows 165 GB/tape, with transfer rates of 
16MB/sec. A 27 terabyte robotic jukebox is available that 
will store 100 million 300 page books in compressed format. 
As an example a project to establish a 1 point/sq. meter 
digital terrain model (DTM) for the land portion of the earth 
covering 1.0 x 10% km? would contain 10" points. It 
requires approximately 16 bits to document each elevation so 
the total database would be 1.6 x 10 bits (equivalent to 
1200 digital D2 tapes or two DD2 robotic jukeboxes). A 
further example of a sustainable development database for 
South America would contain 3-15 terabytes (3-15 x 10'?) or 
one DD2 jukebox. Storage is thus vastly improved over what 
we could envision in 1990 and the technology is finally 
reaching a level where hemispheric and global GIS databases 
of sufficient detail for planning are finally feasible. 
Database management systems are also improving in 
efficiency. Distributed databases with two phase commit are 
finally here, allowing data to be stored in multiple user 
locations yet accessed over networks. Fiber optic networks 
will be needed for large data volumes. Most GIS systems 
have their graphics database separate from their associated 
attributes. This is unfortunate (but understandable for 
performance reasons) since it is easy to get the data out of 
synchronization, and, with large databases it will be difficult 
to maintain database integrity. Hopefully, both graphics and 
attribute data can be integrated in one database on more GIS 
in the future. 
A conceptual and fundamental GIS operation is shown in 
Figure 1. The primary objective of any GIS is to collect 
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