Geographic information system
GIS
Geographical information system (GIS)
 A computer application that helps us to access and use
geographical information.
 It helps us to access and use information such as
information about drainage, settlement, land uses and
relief.
Remote sensing
 This is the collecting of information about objects from a
vertical distance.
 It involves using aero planes, drones, hot air balloons and
satellites to collect information about objects.
Advantages of remote sensing.
 It is cheap
 It can be used in places that are difficult to access by
people like mountains
 It is time saving
Vector and raster data
Vector data
 This is Data represented in form of points, lines and
polygons or areas.
 Topographic maps are made up of vector data.
 Features are inform of points, lines or polygons
 Point features- settlements, spot heights, trigonometrical
stations, police station
 Line features- rivers, roads
 Polygon features- dams, lakes, cultivated land
Raster data
 This is Data represented inform of digital images.
 Orthophoto maps are an example of raster data
Pixels
 These are the smallest building blocks of digital images or
the smallest unit of raster data
 The higher the pixel image, the more clear the image
Spatial resolution
 This is the amount of detail shown in a digital image
 It refers to how clear a digital image is
 High spatial resolution- images that show a lot of details
Images that are very clear
 Low spatial resolution- images that show less details
Images that no clear
Attribute and spatial data
Attribute data
 This is data that describes the characteristics of features.
 An attribute is a characteristic of a feature
Forexample,
•
It is a Periodic river
•
The river has a dendritic drainage pattern
•
The river has a high drainage density
Spatial data
 This is Data that describes the location of a feature or
object
 The location of a feature is described by its grid reference
Data layers
 This is a set of information showing a specific theme.
Examples of data layers

Drainage of a place

Relief of a place

Settlements in a place
Data layering
 This refers to the Placing of data layers on top of one
another

A topographic map is an example of data layering
Paper GIS.
Data integration
 Combining different sets of data together.
Gis components
 These are the different parts that make up the GIS
Examples of components
 Software
 Hardware
 Users
 Data
 methods
Buffering
 Demarcation of an area around a feature
Data manipulation
 This is data that has been processed and converted
making it easier to use.
Querying
 Ability to ask and answer questions about geographic
features and their attributes and relation between them
Data standardisation
 Making data similar for analysis