The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B4. Beijing 2008
Some basic GIS functions
Essentially, GIS provides a means of taking many different
kinds of information, processing it into compatible data sets,
combining it, querying and displaying the results on a map.
Some standard GIS capabilities include:
• Integrating maps based on different scales, map projections,
or legends;
• Changing of scale, projections, legend, annotations, etc.;
• Overlaying different types of maps of a particular area to
make a new map that combines the attributes of the
individual maps. For example, a vegetation map could be
overlaid on a soil map, as shown in the figure above. This
in turn could be overlaid on a map showing length of
growing season, thereby producing a land suitability map
for a given crop;
• Generating buffer or proximity zones around lines or
polygons on a map. This technique is used to find areas
within a given distance from roads, rivers, etc., or from
certain thematic conditions. These buffer zones can in turn
be used as another layer in overlay operations;
• Querying spatial and attribute databases.
Satellite Remote Sensing
Satellite imagery in digital format allows for the acquisition of
environmental data and land occupation patterns and features
over large areas. Sensors in satellites record multispectral data
from different wave bands in digital format. Different features
of the terrain reflect differently in each waveband, allowing for
their recognition in the images. The digital image is fed into the
computer, where it is stored. The digital images can then be
displayed and further processed to extract the desired
information. They may also be integrated with other types of
data and information within a GIS.
The information found within a digital image is contained in a
grid constructed of spatial units called pixels. Each pixel
number is related to color intensity and brightness. The main
limitations of satellite images are cloud cover (Earth Resources
Satellites pass over the tropical areas early in the morning, a
period when clouds and mist are most prevalent) and resolution.
Even with the best resolution available (pixels < 30 m), it is not
possible to see houses, to adequately classify some types of
agricultural practice, or to localize some breeding sites. Some of
these problems may be circumvented using satellite navigation
receivers.
By using the data from the different wave bands, it is possible to
identify and track environmental characteristics. Vegetation,
land-use patterns, surface waters, quality and humidity of the
soil, roads, built-up areas, and climatic changes may all be
monitored by satellite.
Satellite Navigation System (SNS)
The satellite navigation system (SNS) was originally designed
to enable a user to obtain an instantaneous three-dimensional
position, anywhere on the earth, at any time, under any weather
condition. Clock information in satellites is emitted by radio
wave.
The difference between the time when a message is sent and the
time when the message is received allows for the calculation of
the distance between the receiver and the satellites. Since the
orbits of the satellites are known, exact positions can easily be
calculated.
The SNS can be used in a number of ways to calculate absolute
and relative positions with varying degrees of accuracy. The
complete system consists of 24 satellites that are distributed in
such a way that an adequate number of satellites is available for
positioning at any given time.
When associated with a GIS, a SNS receiver is a powerful
mapping tool. It can provide quick and accurate positioning of
terrain features and dynamic mapping. The data received can be
transferred to a computer and read by a GIS, where it is
transformed into map format.
APPENDIX 2: GIS Applications
(http://www.geography.wisc.edu/sco/gis/applications.htm
1)
Environment
Infrastructure and Utilities
Business Marketing and Sales
Computer Cartography
Land Information
REFERENCES
Ak9akaya, H. R. (1992) Population viability analysis and risk
assessment. In Wildlife 2001: Populations, D.R. McCullough
and R.H. Barrett (eds), Elsevier Publishers, London.
Aspinall, R. and Veitch, N. (1993). Habitat mapping from
satellite imagery and wildlife survey data using a bayesian
modeling procedure in a GIS. Photogrammetric Engineering
and Remote Sensing 59(4): 537-543.
Bretas G., Geographic Information Systems for the Study and
Control of Malaria. Online:
http://www.idrc.ca/books/focus/766/bretas.html
Goodchild. M. (1993) Introduction in Environmental Modelling
with GIS. Oxford University Press London.
Heywood, I., Cornelius, S. and Carver, S (1998) An
introduction to Geographical Information Systems. Pearson
Education Limited, England, pp 279.
Houston-Galveston Area Council (C & E Geographic
Information System): What is GIS? Online:
http ://www. hgac. cog. tx. us/geography/cep/whatis. htm 1
Huxhold, W. E. (1994) Long range planning for a
multidisciplinary gis environment in an academic setting. In
URISA (1994) Urban and Regional Information Association,
p732-744
Johnson, L. B (1990) Analysis of spatial and temporal
phenomena using geographical information systems. Landscape
Ecology 4(1): 31-43..
Johnston, C. A. and R. J. Naiman (1990) The use of a
geographic information system to analyze long-term landscape
alteration by beaver. Landscape Ecology 4: 5-19.
Karimi, H. A. (1999) Parallel Geographic Information Systems
for Solving Complex Environmental Problems. Supercomputing
Center of North Carolina. Online:
http://es.epa.gov/ncer/progress/grants/96/high/karimi99_l.html.
Keller, J. K. (1990) Using aerial photography to model species-
habitat relationships: the importance of habitat size and shape.
pp 34-46. in Mitchell, R. S., C. J. Sheviak, and D. J. Leopold
eds. Ecosystem Mangement: Rare species and significant
habitats, vol bull 471. New York, New York State Museum.
77