An introduction to Geographical Information Systems fourth edition
Chapter 1 to 8
CHAPTER 1: what is GIS
GIS for:
Location: where is the nearest bookshop
Patterns: where do high concentrations students live in this city?
Trends: where have changes to the population of polar bears occurred?
Conditions: where is there flat land within 500 m of a major highway?
Implications: if I move to a new home in this location, how far will I be from the office?
GIS has been used since 1960
The definition of GIS depends, according to Pickles, on who is giving it and their background and
viewpoint.
Rhind for example says: GIS is a computer system that can hold and use data describing places on the Earth’s
surface.
In general the definitions of GIS cover three main components:
GIS is a computer system
GIS uses spatially referenced or geographical data
GIS carries out various management and analysis tasks
The Department of the Environment(1987) lists that a well-designed GIS should provide
1. Quick and easy access to large volumes of data
2. The ability to
o Select detail by area or theme
o Link or merge one data set with another
o Analyse spatial characteristics of features in an area
o Model data and assess alternatives
3. Output capabilities (maps, graphs…) tailored to meet particular needs
GIS:
Computer system
Software
Spatial data
Data management and analysis procedures
People/organization
Computer system
GIS run on computer systems.
Software
Without software GIS can’t analyse, manage and output your data
Spatial data
GIS is designed to handle spatial data.
,Data management and analysis procedures
Because GIS should perform data input, storage, management and analysis
People/Organization
There must always be people to plan, implement and operate the system as well as make decision
based on output.
Elements that are essential for effective GIS operation
The presence of a processor with sufficient power to run the software
Sufficient memory for the storage of large volumes of data
A good quality, high-resolution colour graphics screen
Data input and output devices
Data input: process of converting data from its existing form to one that can be used by the GIS
IMPORTANT
GIS can be used to add value to spatial data
It is difficult to explain GIS because it depends on who is giving the definition and their point of
view. Also definitions of GIS are likely going to change quickly as technology and applications
develop further.
Components of GIS: computersystem, software, people, spatial data, data management and analysis
procedures
Spatial data: information about position, connections with other features and details of attribute data
Attribute data: information about amounts, speed, temperature, numbers and direction
Spatial referencing: forms of spatial data to get information about a position
Spatial entities: help to simplify spatial data. Entities are components to help data organization. Three
types: lines, areas and points.
Geographic Information Science is the science behind the System
, CHAPTER 2: spatial data
Data: observations we make from monitoring the real world. Data are collected as facts or evidence
that may be processed to give them meaning and turn them into information.
Data are raw numbers, numbers without meaning. To make numbers useful you need to add context,
for example what the data refers and which scale or unit of measurement it has. With these details data
become information. information is data with meaning and context added.
Primary data: data collected through first-hand observation.
Secondary data: collected by another individual or organization
All primary and secondary data have three modes or dimensions: temporal, thematic and spatial
Example: incident in
Three Pines Valley on 14
february 2002
Temporal: 15:30 hrs 14 In GIS thematic data are referred as non-spatial or attribute data
February 2002
Thematic: wet slab
avalanche triggered by two Scale gives an indication of how much smaller than reality a map is.
off-piste skiers
- Ratio scale= 1:50000
Spatial: Three Pines Valley, - Verbal scale= 1 cm represents 50 m
south-facing slope - Graphical scale= *a scalebar* drawn on the map
Small-scale maps (1:250,000) are those that cover large areas. Large-scale maps (1:10,000) cover
small areas and contain large amounts of detail.
Scale-related generalization: relationship between scale and detail. How larger the scale how more
detail.
Spatial referencing: used to locate a feature
Several methods of spatial referencing exists, but it can be grouped in three categories:
- Geographic co-ordinate systems;
- Rectangular co-ordinate systems;
- Non co-ordinate systems.
Geographic co-ordinate systems: latitude and longitude
Rectangular co-ordinate system: to use data in the two-dimensional form. A grid is placed on top of
the map. For example, UK Ordnance Survey’s National Grid
Non co-ordinate systems: provide spatial references using a descriptive code rather dan coordinates.
For example postal codes.
Problems of spatial referencing:
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