The document discusses spatial data, which identifies geographic locations and is used in Geographic Information Systems (GIS). It outlines two primary types of spatial data: vector data, characterized by points, lines, and polygons with advantages such as accurate representation of shape, and raster data, defined by pixel values suitable for continuously changing values. The document also highlights the advantages and disadvantages of both data types and sources for GIS data.

1. Spatial Data
 Prepared By
 Md. Akram Ullah
Lecturer
FIMS,NSTU

2. Spatial data
The data or information that identifies the
geographic location of features and
boundaries.
On earth, such as natural and constructed
features like Ocean, lake, pond etc.
Spatial data is usually stored as coordinate
and topology, and is data that can be mapped.

3. IN GIS THEARE ARE TWO BASIC
SPATIAL DATA TYPES
RASTER
DATA
VECTOR
DATA
IN GIS THERE ARE TWO TYPES OF SPATIAL
DATA TYPES

4. Vector Data
Vector data provide a way to represent real world features within
the GIS environment. A vector feature has its shape represented
using geometry. The geometry is made up of one or more
interconnected vertices. A vertex describe a position in space
using an x, y and optionally z axis. In the vector data model,
features on the earth are represented as:

5. • points
• lines / routes
• polygons / regions
• TINs (triangulated irregular networks)

6. Vector Data
This system of recording features is based on the interaction
between arcs and nodes, represented by points, lines and
polygons. A point is a single node, a line is two nodes with an arc
between them, and a polygon is a closed group of three or more
arcs. With these three elements , it is possible to record most all
necessary information.

7. Points
Polygons
Lines

8. Vector Data
Advantages
• accurately representing true shape and size
• representing non-continuous data (e.g., rivers, political boundaries, road
lines)
• Vectors can store information

9. About topology
• A vector data model uses points stored by their
real (earth) coordinates and so requires a precise
coordinate system. Geographic Coordinate
System Latitude/Longitude Cartesian Coordinate
Systems X,Y Coordinate system

10. Vector Data
Disadvantages:
• The location of each vertex needs to be stored explicitly.
• Vector data must be converted into a topological structure.
• This is often processing intensive and usually requires
extensive data cleaning.
• Updating or editing of the vector data requires re-building of
the topology.

11. Vector Data

12. Vector Data

13. Raster Data
Raster Data – cell –based data such as aerial imagery and digital
elevation models. Raster data is characterized by pixel values.
Basically, a raster file is a giant table, where each pixel is assigned
a specific value from 0 to 255. The meaning behind these values
is specified by the user – they can represent elevations,
temperature, hydrology and etc.

14. Impact of resolution
Portraying large areas at
high precision is
problematic
1-14
90m resolution
10m resolution
*Storage space increases
by the square of the
resolution

15. Advantages:
• Raster is the best way to store continuously changing values
such as elevation, slope.
• Analysis faster and more flexible then vector for many
application.
• Rapid computations ("map algebra") in which raster layers are
treated as elements in mathematical expressions

16. Raster analysis functions
Density
Least cost path
Distance Interpolation
Viewshed
Buffers

17. Raster Data
Disadvantages:
• It is especially difficult to adequately represent linear features
depending on the cell resolution.
• Network linkages are difficult to establish.
• Processing of associated attribute data may be cumbersome if
large amounts of data exists.
• Raster maps inherently reflect only one attribute or
characteristic for an area.
• Most output maps from grid-cell systems do not conform to
high-quality cartographic needs.

18. GIS data models
1-18
Vector model
Raster model

19. Sources for GIS data
 Analog maps
 Aerial photographs
 Satellite image
 Ground survey with GPS
 Reports and publications
Remote Sensing and GIS in Water Management © Dr. Saiful Islam, IWFM, BUET