Internet friendly;
not tied to any proprietary GIS;
specifically designed for feature-based spatial data;
open to use by anyone;
compatible with industry-wide IT standards.
It is also likely to set the standard for the delivery of spatial information content to PDA and WAP devices, and so form an important component of mobile and location-based (LBS) GIS technologies.
Amongst the organizations adopting GML is the Ordnance Survey (OS), the national mapping agency for the UK. The OS will deliver DNF (Digital National Framework) data in GML. DNF is a version of the OS’s large-scale topographic database that will eventually
encompass all types of spatial data and all data scales. In the DNF nearly 230,000 tiles of large-scale topographic data have been merged into a single, seamless topologically structured point, line and topographic database containing information on buildings, boundaries, roads, railways, water and other topographic features. Each feature in the DNF is assigned a unique 16-digit identifier that allows it to be unambiguously referenced and associated with other features.
By adopting GML, the OS is making the DNF acces- sible to more software systems and users than would be possible using any other single data standard.
(Sources: Holland, 2001; GISNews, 2001) BOX 2.12
REVISION QUESTIONS
Explain the difference between data and information.
What are the three basic spatial entities and how are these used to portray geographical features on paper maps and in GIS?
Explain the differences between geographic and rectangular co-ordinate systems. What are their relative advantages and disadvantages?
Explain what is meant by adjacency, containment and connectivity.
Why is a knowledge of the different scales of measurement important in GIS?
Explain the importance of map projections for users of GIS.
Describe the characteristics of three sources of spatial data.
Using examples, outline the importance of stan- dards for spatial data.
FURTHER STUDY – ACTIVITIES
For a project you are involved in, list your data sources. Review each one and identify any issues about scale, entity definition, generalization, projections, spatial referencing and topology that you think might be relevant.
Compare large- and small-scale maps of the same area. Select a small area and note the differences in how common features are represented on the two maps. How is this controlled by generalization?
Use a world atlas to compare global and regional map projections.
Use the national statistics sites in the list of websites below to find an up-to-date population figure for New Zealand and the Netherlands.
How is the current population total calculated?
Calculate spatial references for your home or office using latitude and longitude and the local grid co-ordinate system.
Use the web to find aerial photographs and satellite imagery for your home town or an area with which you are familiar. Does the resolution of the image allow you to discern familiar locations or features?
Can you notice the effects of edge distortion, time of day/year and so on in your image?
Use the web to find and compare satellite images captured by different sensors.
FURTHER STUDY – READING
Gatrell (1991) provides a good, thought-provoking introduction to the concepts of space and geographi- cal data that is a good starting point for anyone coming to GIS from a non-geographical back- ground. Robinson et al. (1995) and Keates (1982)
the generality with which these entities have been modelled; and
the topological structure used to represent the relationship between entities.
In some data sources, one factor will dominate; in others it will be the interplay of factors that gives the data their character. Appreciating the main charac- teristics of spatial data is important because these characteristics will determine how the data can be used in building a GIS model. For example, data col- lected at different resolutions should only be integrated and analyzed at the resolution of the
coarsest data set. In the Zdarske Vrchy case study the 30 m by 30 m resolution of the land use map gener- ated from TM satellite data dictated the resolution of the database for analysis.
Therefore, GIS models are only as good a repre- sentation of the real world as the spatial data used to construct them. Understanding the main characteris- tics of spatial data is an important first step in evaluating its usefulness for GIS. The next step is to understand how these data can be stored in a form suitable for use in the computer, as this will also influence the quality of the GIS model.
CONCLUSION
provide comprehensive coverage of the subject of cartography from a more conventional viewpoint.
Monmonier’s book How to Lie with Maps (1996) offers a comprehensive and very readable introduction to the potential pitfalls of displaying data in map form.
The discussion is just as applicable to maps on the computer screen as those on paper. Subjects such as scale, projections and generalization are covered in detail. A good discussion on UK spatial referencing can be found in Dale and McLaughlin (1988);
DeMers (2002) provides a comparable review for the USA. The Chorley Report (Department of the Environment, 1987) provides brief details of post- codes and recommendations for use of spatial referencing in the UK. Raperet al. (1992) discuss the whole issue of UK postcodes in considerable depth and provide examples of address formats and post- code systems in a number of other countries including Austria, Germany, the Netherlands, Spain, Sweden and the USA. A similar discussion on the US ZIP code, though not in the same depth, can be found in DeMers (2002).
Comprehensive coverage of the principles and applications of remote sensing can be found in Curran (1989), Clayton (1995) or Gibson and Power (2000). Curran (1989) contains a particularly useful chapter on aerial photography that discusses the characteristics and interpretation of aerial photo- graphs. A good introduction to GPS and its importance for GIS can be found in Kennedy (1996).
Seegar (1999) offers the basic principles of geodesy relevant to GPS. Up-to-date information on GPS can be found in publications such as GPS World.
Clayton K (1995) The land from space. In:
O’Riordan T (ed.)Environmental Science for Environmental Management. Longman, London, pp. 198–222
Curran P (1989) Principles of Remote Sensing.
Longman, London
Dale P F, McLaughlin J D (1988) Land Information Management: An Introduction with Special Reference to Cadastral Problems in Third World Countries. Clarendon Press, Oxford
DeMers M N (2002) Fundamentals of Geographic Information Systems. Wiley, New York
Department of the Environment (1987) Handling Geographic Information. Report of the Committee of Enquiry chaired by Lord Chorley. HMSO, London
Gatrell A C (1991) Concepts of space and geo- graphical data. In: Maguire D J, Goodchild M F, Rhind D W (eds) Geographical Information Systems:
Principles and Applications. Longman, London, vol. 1, pp. 119–143
Gibson P and Power C H (2000) Introducing Remote Sensing: Digital Image Processing and Applications.
Routledge, London
Keates J S (1982) Understanding Maps. Longman, London
Kennedy M (1996) The Global Positioning System and GIS: An Introduction. Ann Arbor Press, Ann Arbor, Michigan
Monmonier M (1996) How to Lie with Maps.
University of Chicago Press, Chicago
Raper J F, Rhind D W, Shepherd J W (1992) Postcodes: the New Geography. Longman, Harlow, UK
Robinson A H, Morrison J L, Muehrecke P C, Kimerling A J, Guptill S C (1995) Elements of Cartography, 6th edn. Wiley, New York
Seegar H (1999) Spatial referencing and coordi- nate systems. In: Longley P A, Goodchild M F, Maguire D J, Rhind D W (eds) Geographical Information Systems. Wiley, New York, vol. 1, pp. 427–36
WEB LINKS
National Mapping Agencies and other GIS data sources:
United States Geological Survey http://www.usgs.gov
Ordnance Survey, UK
http://www.ordnancesurvey.co.uk
Centre for Topographic Information, Canada http://maps.nrcan.gc.ca/
Geoscience, Australia http://www.ga.gov.au/
Eurographics, European National Mapping Agencies http://www.eurogeographics.org
The Geography Network
http://www.geographynetwork.com/
GeoCommunity GIS Data Depot http://data.geocomm.com/
Map projections:
Cartographical map projections http://www.progonos.com/furuti/
MapProj/Normal/TOC/cartTOC.html
Gallery of map projections
http://www.ilstu.edu/microcam/
map_projections/
Census agencies:
United States Census Bureau http://www.census.gov/
National Statistics, UK
http://www.statistics.gov.uk/
Statistics Netherlands
http://www.cbs.nl/en-GB/default.htm
Australian Bureau of Statistics http://www.abs.gov.au/
Statistics New Zealand
http://www.stats.govt.nz/default.htm
GPS:
GPS World
http://www.gpsworld.com/gpsworld/
UK National GPS Network http://www.gps.gov.uk/
Garmin, What is GPS?
http://www.garmin.com/aboutGPS/
Data standards:
Federal Geographic Data Committee http://www.fgdc.gov/
Open Geospatial Consortium http://www.opengeospatial.org/
Visit our websitehttp://www.pearsoned.co.uk/heywood for further web links, together with self-assessment questions, activities, data sets for practice opportunities and other interactive resources.