GIS data sources, types and their projections for
environmental management
Outline
Types of GIS data
Sources of Data for Environmental management
GIS Data Types
Geographic Data Types
1. Spatial Map Data – this is the location and shape of an object or feature.
2. Attribute Data – This is Descriptive data. It identifies what the map data is.
• These are all considered non-spatial because by themselves they do not pinpoint a
location.
• It can be qualitative (nominal data) or quantitative (ordinal, interval or ratio data)
3. Image Data – satellite image, aerial photographs and scanned maps fall
into this category
GIS Data Models/Formats
• Vector Data – (geo-objects) features are represented as Points, Lines,
Polygons
• Raster Data – Store features on a grid or as pixels
Cont…
• Models are ways of storing geographic information in the GIS.
• By using data models we can represent the real world in a way that
the computer can understand and do analysis that hold true to the
real world.
• The two most common data models are Vector and Raster.
Cont…
• Vector Data (Database oriented)
• Represents the world using points, lines and polygons, these are useful for storing
data and representations of features such as buildings, trails and roads.
• Examples of vector data models are Shapefiles (Esri), Triangulated Irregular
Networks (TINs) and AutoCAD (.dxf files).
• Points are non dimensional defined by x , y coordinates.
• Polygons are the enclosure of one or more lines
• Points and elevation = Line e.g. pole
• Lines and elevation = A vertical polygon e.g. a wall
• Polygon and elevation = A 3 dimensional feature e.g. volume
Cont…
Vectors are more database oriented and are very good at representing
features such as rivers, boundaries and roads.
Advantages Disadvantages
o Compact data structure Complex data structure
o Suitable for cases where data must closely represent Overlaying data is not simple
hand drawn maps It doesn’t represent data over surfaces
o Have an accurate advantage
well e.g. topography
o Good for storing data that need topological
information – they can store information of how a
feature connects to others e.g. road networks
o Good system for plotting data
Sources of vector data: GPS Surveys, manual digitizing, analyzed raster
Cont…
Raster Data (Analysis oriented)
• This model uses grids to store map data.
• It creates a continuous surface defined by series of discrete grid cells.
• Each cell has a value that represents attribute data at that location.
• Cell size determines resolution.
• The smaller the cell size the better the resolution.
• For example a 50 meter Landsat image means that each cell is 50 meters on the ground.
• A smaller cell size means more details.
• Raster grids can analyze and retrieve data quickly.
• This is because the raster structure closely resembles that of a computer’s..
Cont…
• The data is a continuous representation of a study area and is therefore suited to data that is
continuous such as terrain, vegetation and natural resources.
Advantages
• Overlaying easily done
• Variability is well represented
• Easy to understand
Disadvantages
• Not a compact data structure/needs large space for storage
• Connective relationships are difficult to represent
• Blocky appearance
• Sources – User interpolation of vector data, commercially available
Cont…
Metadata ‘..the who, what, when, where, how and why of the
dataset’ - [raster data]
• Often referred to as “data about data”, metadata is a summary
description of the data set it is included with.
• This includes notes on the content, quality, type, creation, condition,
origin/ source organizations, data format, accuracy and spatial
information about the dataset.
• It can be stored in any format such as database files or text format.
GIS Data Sources
• GIS handles different data from different
sources to produce new information
• Geospatial data acquired using different sources
• Common data sources:
Paper maps,
Existing digital data(web based and from
other database system)
Aerial photographs
GPS (Global Positioning Systems)
Surveying instruments, e.g. Total Station
Imageries from Remote-sensing
satellites/ Earth observation satellites
and
Laser Scanners, usually mounted in
Aircrafts
Drones and UAVs
Cont…
Cont…
• Earth observation data: most commonly used data sources
• Earth observation is gathering of information about the planet earth
• Earth observation satellites are satellites specifically designed to
observe Earth from space
• Data from Earth observation satellites/ Remote sensing satellites are
processed into images: remote sensing images, satellite imageries
or satellite data
• Data collected using GPS can be imported in to a GIS system
• Global Positioning Systems (GPS) used for data collection and
capture
• GPS is a space-based satellite navigation system that provides
location and time information (uses WGS84 coordinate sytem)
Cont…
GPS is one of the Global Navigation
Satellite Systems (GNSS);
Other GNSS include: GLONASS
(Russia), Galileo(Europe), Beidou
(China)
Existing digital data are available in different formats
Features extracted from satellite images using image
processing techniques, already existing in different
databases
Most GIS databases created with data converted from paper
maps/ Arial photo
Digital maps, datasets and image data are available in the
Internet, in different data portals, web based data, etc
Cont…
Thank You
