Spatial data for GIS

Also known as geospatial data or geographic information it is the data or information that identifies the geographic location of features and boundaries on Earth, such as natural or constructed features, oceans, and more. Spatial data is usually stored as coordinates and topology, and is data that can be mapped.

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 . S patial data is usually stored as coordinate and topology, and is data that can be mapped. s

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. U pdating 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. R apid 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. N etwork 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