GIS: A System and a Subject Three Views of GIS Elements of a GIS Geographical Data Models And Databases Geographical Features Disaggregation and Analysis Operations of GIS GIS Applications in the Marine Environment ADVANTAGES DISADVANTAGES GIS application for Port Development Bibliography
GIS: A System and a Subject
The term 'Geographical Information System (GIS)' and its synonym ‘Geographic Information System' used in North America, is frequently applied to geographically-oriented computer technology and integrated systems used in substantive applications. More recently, it has also been used to describe a new discipline which is generating massive interest world-wide.
GIS are seen by many as special types of information systems. In general, information is derived from the interpretation of data which are symbolic representations of features. The value of information depends upon many things including its timeliness, the context in which it is applied and the cost of collection, storage, manipulation and presentation.
Three Views of GIS
The various ideas about GIS can be synthesized and presented as three distinct, but overlapping, views. These can be termed the map, database and spatial analysis views. Other views of GIS have been suggested, the most notable being the application view in which the idea of GIS as the technology to deal with global scientific problems is prominent, though this and other views are not widely held currently.
The Map View
The map view focuses on cartographic aspects of GIS. Supporters of this view see GIS as map processing or display systems in which each data set is represented as a map (also called a layer, theme or coverage). The maps are usually manipulated by a function that might add or subtract two maps or search for patterns in a single map. The output from these operations is another map. Topographic and thematic mapping agencies also support the map view and place great emphasis on the ability of GIS to produce high quality maps and charts.
The Database View
The database view of GIS emphasizes the importance of a well designed and implemented database. A sophisticated database management system is seen as an integral part of a GIS. This view predominates amongst members of the GIS community who have a computer science background. Applications which record transactions and require the frequent use of simple queries are particularly suited to this approach. Complex analytical operations requiring the use of many types of geographical data can as yet only be undertaken with difficulty.
The third view of GIS emphasizes the importance of spatial analysis. This view focuses on analysis and modeling in which GIS is seen more as a spatial information science than a technology. Although current proprietary GIS software systems have limited functionality for spatial analysis, this is emerging as a major development area. This view looks likely to become the most widely accepted by the GIS community and already it is being used to differentiate GIS from other information systems.
Elements of a GIS
GIS comprise five basic elements: computer hardware, computer software, data, liveware (or people) and procedures (or an institutional context).
The hardware element can be almost any type of computer platform such as: relatively modest personal computers (PCs); high performance workstations; minicomputers; and mainframe computers.
In addition to the standard input,- storage and output devices, specialist peripherals are required for data input leg, scanners and digitizers), data output leg, plotters) and, sometimes, data storage and processing.
There is now a great deal of what claims to be GIS software, much of which has been developed to very sophisticated levels. Major software packages have several hundred commands and a wide variety of functionality. Although there are variations in the organization and capabilities of GIS software, three basic designs have evolved called the file processing, hybrid and extended designs. In the file processing design, each data set and function is stored as a separate file and these are linked together during analytical operations. Examples of systems using this design are IDRISI and MAP. In the hybrid design, attribute data are stored in a conventional database for geographical data. ARC/INFO and Genamap are examples of the hybrid design. In situations where attribute data are stored in a relational DBMS these are sometimes referred to as geo-relational. In the third design type, the extended DBMS, both the geographical and the attribute data are stored in a DBMS which is extended to provide appropriate geographical analytical functions. Well known examples using the extended design are SYSTEM9 which extends the EMPRESS DBMS and Smallworld GIS which uses a bespoke DBMS.
The third important element in a GIS is the data. In many respects data are a crucial resource. Geographical data are very expensive to collect, store and manipulate because large volumes are normally required to solve substantive geographical problems. Although estimates vary, it is not uncommon for the cost of data collection to exceed the cost of hardware and software by a factor of two. Until relatively recently there has been a paucity of data for use in GIS. However, four types of activity have improved this situation: the greater use of machine based recording and data collection; the widespread use of images from remote sensing satellites; the ambitious national mapping programs of many countries; and the collaborative international ventures which aim to create global databases. The success of these activities now means that the significant problems caused by large data volumes have to be addressed.
Liveware, that is the people responsible for designing, implementing and using GIS, is the fourth element. Without properly trained personnel, with the vision and commitment to use GIS, little will be achieved.
Procedures or Institutional Context
The final and most significant GIS element concerns the procedures or institutional context in which GIS operate. Without the necessary commitment of key individuals and organizations, GIS will not Progress as far and as fast as it should. Many organizations have well established working practices and ideals which need to be addressed before GIS can become successfully incorporated.
Geographical Data Models And Databases
The central focus of a GIS is a spatial database comprising an integrated collection of data about spatial objects and their attributes. A spatial database is a realization of a data model; a basic system of spatial constructs used to describe reality. Two fundamental spatial data models are recognized and these are referred to as the vector and raster (also called tessellation) models. The type of data model employed has a profound impact on the conventions and procedures of a GIS. The selection of data model is influenced by many factors including the software available, the nature of the application, the training of the individual and historical precedent.
In the raster model, geographical features are described as polygonal units of space in a matrix (also called a mesh, lattice grid or array). Usually the polygonal units are regular squares referred to as pixels but regular and irregular triangles and hexagons have also been used.
In the vector model, geographical models are represented as a series of X,Y or X,Y,Z coordinates. The vector model is much more complex than the raster model and is less readily adaptable to cheap microcomputer technology. In the vector model geographical features are represented in continuous space.
In GIS, geographical features are usually defined according to their geographical and attribute data elements. The geographical (also called locational or spatial) data element is used to provide a reference for the attribute (also called statistical or non-locational) data element. For example, administrative boundaries, river networks and point locations of sites are all geographical features used to provide a reference for, respectively, census counts, river water flows, or site elevations. In GIS the geographical and attribute elements are equally important. This is one of the key features which differentiates GIS from other information systems.
Disaggregation and Analysis
The process of describing the geographical features in a study area and creating an abstraction that is suitable for implementing as a spatial database is called data modeling. In spatial data modeling, reality is disaggregated into a series of data layers (also called planes, coverages and map layers). Each data layer normally contains data on one particular theme and frequently, though not necessarily, a single generic geographical feature type.
The features in a data layer must exhaust the space (the background exists as a feature) and features must not overlap. This principle is termed ‘planar enforcement and is particularly important for forming topological relationships.
An important aspect of spatial databases is that these data layers can be related together by geography. The positions of geographical features on all data layers can be compared because the data layers are co-registered.
This fundamental characteristic of GIS means that powerful and sophisticated analytical operations can be carried out on the features in geographical databases. A great deal of time and effort is expended when building GIS in transforming data so that they can be co-registered and analyzed. This process, often referred to as data integration, involves transforming map projections, map scales and the representation of much geographical and attribute data.
Following analysis, it is customary to re-aggregate at least some of the data layers in order to create a suitable map which displays the results of analytical operations in their geographical context.
Operations of GIS
The purpose of GIS analysis is to relate the geographical features on one or more data layer(s) in an attempt to search for evidence of geographical patterns or processes, or to test hypotheses.
The process of relating geographical features on different data layers is often referred to as 'map algebra' or 'map processing'. In map processing the central focus is not the geographical feature, but the map layer on which one or more features reside. At its simplest, map processing involves the interaction of a single geographical feature and a single operator (also called a function). More often it involves at least two geographical features, on more than one map layer, and one or more operators.
The process of relating geographical features on different data layers is called ‘overlay’. Such is the importance of overlay, many believe it is the fundamental GIS operation.
The map processing concept was developed for, and is still typically applied to, raster databases, but there seems no reason why the same concept cannot also be applied to vector databases. The results of map processing are usually output in the form of another map.
GIS Applications in the Marine Environment
Data collected and fed into a GIS system:
- good fishing areas.
- provide information for fishermen.
- types of fish in specific areas.
- governmental planning and prohibition of fishing in areas where rare fish lie or incubate.
- seaways with increased traffic, highly congested areas.
- determine air, sea rescue and pollution prevention bases in areas where most accidents occur.
- seaways with increased traffic, highly congested areas.
- for port development (infrastructure) and building of new ports where necessary.
- population density and trends.
- promote regional development and support with proper port infrastructure.
- main coastal touristic attractions.
- determine areas where marina and beach developments would achieve major results.
- main coastal touristic attractions.
- determine areas suitable for water activities (sports, boat trips, etc.).
- sea sediment reports.
- combinations of sediments may reveal the presence of useful resources (oil)
- reports of archeological items.
- maps for divers, for archeological research.
- navigational information.
- traffic schemes, information about wrecks, ports, marinas, buoys, etc.
- weather information, winds, sea waves, etc.
- to determine sea routes by avoiding bad weather.
GIS has found its way into modern technology through the services it provides:
1. collection, storage, interpretation, manipulation and presentation of data;
2. cartographic aspects, topographic and thematic mapping;
3. to deal with global scientific problems;
4. database for global features and data;
5. performs complex analytical operations requiring the use of many types of geographical data;
6. has been easily adapted to PC technology and is available for all levels of research;
7. powerful and sophisticated analytical operations can be carried out on the features in geographical databases;
8. relates the geographical features on one or more data layer(s) in an attempt to search for evidence of geographical patterns or processes, or to test hypotheses;
The use of GIS is impossible or at least non-productive without the presence of qualified and experienced persons responsible for designing, implementing and using GIS. This is a problem since not many scientists have acquired expertise on the specific system so far;
Geographical data are very expensive to collect, store and manipulate because large volumes are normally required to solve substantive geographical problems. Although estimates vary, it is not uncommon for the cost of data collection to exceed the cost of hardware and software by a factor of two. At the same time, data must be accurate since the slightest deviation from reality would lead to improper research results and conclusions;
A great deal of time and effort is expended when building GIS in transforming data so that they can be co-registered and analyzed. Hence, although the processing time (data manipulation) is very short, the total time is considerable in order to achieve the required results.
GIS application for Port Development
- samples of seabed sediments and bottom configuration;
- speed and direction of winds, waves, tidal effects, currents;
- depth of area;
- density of salt water;
- special sea life present at the location;
- produce maps showing the different characteristics of each factors involved in the area;
- produce maps which show the interaction of the above elements and their effects;
Data used for determining:
- where dredging is necessary;
- where weather protection is necessary and at what level (protective walls, etc.);
- where docks and quays should be built (adequate depths, no rocks);
- port entrance configuration (protection from weather factors and easy access);
- where special care must be shown not to disturb the natural sea life;
- the location of shore equipment;
Introduction to GIS - The ARC/INFO Method
B.William Hickin, David J. Maguire, Alan J. Strachan.
Green Peace information booklet
Endangered species in Greece - 1995