Julian Conrad, Simon Hughes and John Weaver
6.3 Geographical Information System in map production
Maps can be compiled manually or by computer, depending on the size of a project and the financial and staff resources of a map-maker. Although the Geographical Information System (GIS) is the system of choice nowadays, considerations of cost, time, and professional resources may limit the production of maps in a GIS format. For example, if the study is not part of a long-term assessment or program, or if only a small area is studied, then the use of manual techniques Zaporozec, 1994). However, for large projects with a great amount of data, mapping may be more efficiently conducted by using a GIS.
6.3.1 GIS components and functions
The most common form of digital mapping technology used today is the Geographical Infor-mation System (GIS), which can be very helpful by rapidly providing systematical inforInfor-mation.
Simply put, GIS is a user interface for spatial data bases. This technology makes it possible to combine layers of digital data from different sources and to manipulate and analyse how the different layers relate to each other. An alternative description of GIS is: ‘an organized collection of computer hardware, software, geographic data, and personnel designed to efficiently capture (record), store, update, manipulate, analyse, and display all forms of geographically referenced information’ (ESRI, 1994).
Major advances in the availability and functionality of GIS software have seen this highly practical and user-friendly mapping technique being implemented throughout the world. Foreign aid programs, government surveying departments, and environmental organizations across Africa, Asia, and Latin America have increasingly taken up GIS as the mapping tool of choice in a wide variety of disciplines. Many of these organizations, some utilising remote sensing tech-nology, have completed many projects in fields that include transportation, environmental science, ecology, meteorology, and geology, which parallel and in some cases exceed those completed in the developed world.
Digital spatial data are commonly a vector graphic in the form of a point, line (arc), or polygon with attributes attached in a standard data base file. This spatial information is often digitised from existing maps or remotely sensed data. The attributes are either joined from a look-up table or manually input into the data base. These attributes can vary from a simple identification number (ID) to many fields of descriptive information. The GIS will commonly feature a Graphical User Interface (GUI) to assist the user in manipulating the data. The layers can be combined into a viewing window and the order within the layering system changed to assist with analysis. The attributes allow the user to query or classify the digital data in a display according to specific criteria. For example, if point contamination sites are digitised from a map, attributes can be applied to each section point either during the digitising process or at a later stage. These attributes can be used to describe each contamination source (Fig. 6.11). Features or elements in the view can also be labelled in specific styles using the attributes.
An integral part of most contemporary GIS software packages is a layout or map-making Groundwater contamination inventory
option. This allows the user to compile maps from the data views that they have created. More complex products automate the addition of cartographic elements such as scale bars, north arrows, and measuring grids/graticules. Dynamic links between the digital features in the data view and the map layout not only allow the data to be shown in their predefined format, but assist in the creation of legend keys on the map. Used correctly, these functions allow the creation of complex maps whilst eliminating human error. Whether used in government, business, military, or a host of other applications, a GIS provides the means to examine, and to map, relationships in ways never before possible. Further assistance to the cartographer exists in GIS packages in the form of a wide variety of national and international geodetical standards, map unit presets, and view/layout scale relationships.
6.3.2 Hardware requirements for GIS
Spatial data sets are commonly not large digital entities in comparison to image (raster) data. The graphics element and index to the data base are relatively small, usually less than 1 Megabyte (Mb) in size, depending on the complexity of the feature they represent. The number of fields and records of the data base element usually determines the overall size of the spatial data set.
FIGURE6.11 Vector attributes in spatial data and associated attribute data
Complex data sets can be in the range of 10–20 Mb. Hence, if manipulating numerous layers of information in a GIS, disk storage space is an important consideration. If data input is necessary, a digitising. tablet will be required to transfer hard copy information into digital data.
As GIS packages now feature more complex display and analysis features, they are often processor-intensive, often requiring a minimum of a Pentium microprocessor and 64 Mb of RAM.
Refresh rates of the GUI are improved with the use of more capable microprocessors and better graphics cards and memory. Relational Database Management Systems (RDBMS) serving data to a large group of GIS users require very large storage capacity and fast computer servers.
6.3.3 GIS software packages
There is an ever-increasing market for GIS software packages ranging from desktop products to large process-intensive systems and spatial data base engines (Table 6.4). As with many sectors of the software development industry, the GIS packages currently available exhibit similar capabilities, differing mainly in the data models upon which they rely.
In keeping up with current trends in information technology, ease of use is a common feature of GIS software design. A user with a good knowledge of the fundamentals of GIS theory will be able to create simple and effective maps with little problem.
Most contemporary packages also include a macro or scripting language allowing the development of applications required for spatial analysis or the automation of mundane, repetitive tasks. Apart from removing the necessity for operator participation in batch processing or mapping function, macros/scripts also remove the element of human error from these processes.
Basic GIS software can range in price from as little as US$ 500 to US$ 1,300 for desktop products and in excess of US$ 10,000 for industrial GIS and DBMS products. These prices are approximate and do not include extensions or add-ons. These must be purchased separately.
6.3.4 Additional extensions of GIS
Most GIS software packages now feature additional extension operations that expand the analytical and processing capabilities of the GIS environment. Only some of these facilities are pertinent to groundwater contamination mapping. Whilst some extensions allow the GIS to handle additional data types (raster and image data), some take GIS mapping into a third (z value) and even a fourth dimension (time). Three-dimensional (3-D) visualisation tools can be valuable in the development of an alternate perspective. These 3-D and time tools hold a lot of promise for presenting to decision-makers the results of scenario modelling and predictions.
6.3.5 Advantages and disadvantages of GIS versus other mapping techniques
The primary advantage GIS holds over other mapping techniques is its enormous capacity for attribute information and ability to accurately encapsulate spatial relationships. Computer Aided Design (CAD) software is perhaps the product closest to GIS. It can handle digital spatial data, but is limited in its ability to handle attribute information and has little or no geodetical capability.
CAD spatial capabilities only extend as far as line and point data; and data are exclusively entered and stored in metric units. GIS can also process, display, and project all areal information and all vector formats (lines, points, and polygons).
Dynamic links between GIS software and data bases allow the creation of predefined query environments, in which, as data base attributes are changed through external data base input forms, the map layouts in the query environment respond.
Physical space is another major consideration. A map-server computer can be used to store many thousands of digital data sets that can be served to GIS users through client-server tech-nology over a network. Hence, the equivalent of many thousands of paper maps can be stored on a central server, thus saving space, centralising data storage, and standardising data set use.
A disadvantage of these mapping techniques is the misconception that because the operator is working in a digital environment, accuracy is maintained throughout. There are many factors to
Groundwater contamination inventory
TABLE6.4 Selected GIS and mapping software
A suite of integrated modules covering desktop mapping to corporate GIS.
SIS ActiveX
A suite of modules for embedding within 3rd party applications.
Idrisi32
High-end, raster GIS and image processing for advanced spatial modelling.
CartaLinx
Easy-to-use tools for vector data input, editing, and export.
MapGrafix GIS
The first GIS on the desk top with digitising, printing/plotting, and analytical tools.
IMAGINE
A full suite of products for image mapping, visualisation, and processing.
ArcView extensions
Easy-to-use geographic imaging for ArcView users.
ArcInfo
High-end GIS with new open development environment for customisation.
ArcView
Intuitive desktop mapping and Internet GIS package with unique extensible architecture.
GGP WIN GIS
GIS for local authorities; ideal as corporate networked solutions linking to data bases.
MetaMAP
Turns freehand illustrator into GIS; ideal for quality map production.
Note: Software listed in this table is given as an example for information purposes only. The list is not an endorsement of any company or its products.
consider when working with digital data, the most important of which is data integrity. If a standardised level of data recording and handling is maintained throughout the mapping process, the end product should, to all intents and purposes, engender an equal level of accuracy. Caution should be exhibited when using spatial data of unknown or undocumented origin or accuracy. It only takes one data set of questionable integrity combined with data of a known standard to create results of a false nature. This is a common theme arising in current literature and debate surrounding concerns such as metadata and spatial data standards.
With sufficient support from its hardware environment, a GIS user can manipulate vast quantities of data efficiently and effectively. When considering the cost benefits of available techniques in financial outlay, professional input, resources, and time, no other map-making process can match the speed, accuracy, and reliability of GIS.
To maximise efficiency and capability, training in GIS theory and software use are essential.
A correct introduction to the concepts of GIS and a formal explanation of the data models involved are invaluable when working with spatial data. Such training is usually offered by vendors of software and can often be tailored to the needs of a specific client. These courses can be costly, but if they are prepared correctly and involve the manipulation and mapping of ground-water contamination data, a lot of time and money can be saved.
6.3.6 Image processing software/GIS relationship
Many modern image processing software packages include some GIS functionality, either in the ability to export to GIS-software-supported image formats or actually allowing the use and creation and editing of vector GIS data in their analysis and mapping functions.
Current trends in three-dimensional visualisation are influencing this field. Image drapes, pioneered by image processing software packages, have recently been taken one step further with the ability of some software packages to display spatial vector data and raster data together in a 3-D environment. These processes can reap rich rewards in the identification of relationships not clear in two dimensions.
6.3.7 Serving map data on the Internet
The last few years of the 20th century have seen enormous advances in communications tech-nology. Moving to the forefront of this field is the Internet and its related technologies. Initially designed to deliver text, the browsing technology has been developed to now include graphics, animations, and even stand-alone programs that run within the Web page (Fig. 6.12).
Several of the larger GIS software companies have developed software to drive map-serving over both company Intranets and the Internet. This technology enables:
•
searching for specific site locations;•
displaying and viewing multiple data sets;•
conducting query-based analysis;•
performing data purchases;•
retrieving specialised data services (ESRI,1994).Internet map-serving allows the production of a map in a digital format. It also allows interactive manipulation of geographical data, similar to a normal GIS graphical user interface.
6.3.8 Useful websites addresses for map production
http://www.usgs.org/mac/isb/pubs/booklets/topo/topo.html
FIGURE6.12 A Web-page embedded Java applet that allows display of shape files