Basics of GIS by Basudeb Bhatta Computer Aided Design Centre Department of Computer Science and Engineering Jadavpur University e-governance Training Programme Conducted by National Institute of Electronics and Information Technology, Kolkata 12 May 2016
Definition of GIS GIS is as an information system that is used to input, store, retrieve, manipulate, analyze and output geographically referenced data or geospatial data, in order to support decision making for planning and management of land use, natural resources, environment, transportation, urban facilities, and other administrative records.
Key Components
GIS Themes
GIS is Integration of Spatial and Attribute Data GIS Attribute data Spatial data
GIS is a Set of Interrelated Subsystems Data Processing Subsystem Communication Subsystem Data Analysis Subsystem GIS Management Subsystem Information Use Subsystem
Functions of GIS The questions that a GIS is required to answer are: What is at? Where is it? What has changed? What spatial patterns exist? What if?
Advantages of GIS Advantage over traditional map Advantage over mapping software Advantage over CADD Advantage over AM/FM Advantage over conventional DBMS Advantage of analysis, modelling, presentation and decision making
Limitations of GIS Data for a specific area may lack spatial or temporal continuity. GIS data are relatively expensive than traditional data. Privacy and security issues can sometimes limit distribution of data. Collecting the data can be very time consuming. GIS often relies on the quality of available data, which may introduce serious errors. GIS data may also be subject to misuse or misinterpretation.
Limitations of GIS GIS shows only spatial relationships but does not necessarily explain them or provide absolute solutions, which is the actual need of the user. GIS has its origin in the earth science and computer science. Therefore, solutions derived from GIS may not be appropriate for humanities science/research. Learning time on GIS software and systems can be long, because it easily becomes the objective of the study rather than just a tool. GIS integrates several individual subjects, which demands proper knowledge on all of integrated disciplines. GIS needs specialised computer equipment and software (increasingly becoming less important).
Dimensions of Geographic Data GIS DATA Spatial Thematic Temporal
Spatial Data Model Spatial data model Conceptual Logical Object oriented Object based Field based Raster Vector
Conceptual Data Model Conceptual data model organizes principles that translate the real world into functional descriptions of how phenomena are represented and related to one another. Conceptual data model Object based Field based
Object Objects are with discrete boundaries represented by geometric features.
Field Fields are continuous phenomena such as elevation, temperature, and soil chemistry; they exist everywhere. Surface
Logical Data Model Logical data model provides the explicit forms of representation, which the conceptual model can take. Logical data model Raster Vector
Logical Data Model Raster data are represented as an array of grid cells. Vector data are represented as points, lines, polygons, and volumes. Raster Vector
Raster versus Vector Vector Raster
Object-oriented Data Model This model is based on object-class concept. Real-world objects are used as the basis for abstraction, instead of geometric objects such as points, lines, polygons, or surfaces.
Process of GIS Data capture Encoding raster data Encoding vector data Encoding attribute data Spatial database Attribute database Linking of spatial and attribute data Organizing data for analysis GIS Analysis
Sources of DATA
Geospatial Analysis Spatial or geospatial analysis is the process of modelling, examining, and interpreting model results. The GIS has the capability of carrying out any number of analyses related to any discipline-oriented problems. Common analysis techniques: Database query Geospatial measurement Overlay operations Network analysis Surface analysis Geostatistics Geovisualization
DATABASE QUERY
Database Query Database query just asks to find already stored information. Both raster and vector can be queried.
Vector Data Query There are two types of query that a GIS generally allows on vector data: Query by attribute data Query by spatial data
Query by Attribute Data SELECT <attribute/field name(s)> FROM <table> WHERE <condition statement> Relational: >, <, =,, ; SELECT * FROM road WHERE road_width > 10 Arithmetic: +, -, x, ; SELECT road_width, width + 2 AS new_width FROM road Boolean (logical): AND, OR, NOT, XOR (exclusive OR); SELECT * FROM road WHERE road_width > 10 AND road_type = Highway
Selection by cursor Query by Spatial Data
Query by Spatial Data Selection by graphic objects
Query by Spatial Data Selection by spatial relationship. Containment Selects features that fall completely within features used for selection. Adjacency Selects features that are adjacent to features used for selection. Intersect Selects features that intersect features used for selection. Proximity Selects features that are within a specified distance of features used for selection.
Containment Query by Spatial Data
Query by Spatial Data Proximity - Buffering
Query by Spatial Data Proximity - Buffering
Query by Spatial Data Proximity analysis by time
Raster Data Query Raster may also be queried by the following methods: Query by pixel values of the raster Query by attribute Query by spatial data
GEOSPATIAL MEASUREMENTS
Geospatial Measurements Measurement is also a type of query; however, it does not select any object from the GIS database, instead it gives some statistical/mathematical/geometrical result by measuring the map or resulting a map. Measurement of density Measurement of distance Measurement of neighbourhood
Measurement of Density
Measurement of Distance Physical distance : Distance from Kolkata to Delhi
Measurement of Neighbourhood Thiessen polygon
OVERLAY OPERATIONS
Overlay Operations The capability to overlay multiple data layers in a vertical fashion is the most required and common technique in geographic data processing.
Vector Overlay Overlay operations are based on Boolean logic
Point in polygon Vector Overlay
Line on polygon Vector Overlay
Polygon on polygon Vector Overlay
Raster Overlay
NETWORK ANALYSIS
Network Analysis Network analysis is a range of techniques employed by engineers and planners to study the properties of networks, including connectivity, capacity, and rates of flow. Three major network analysis: Network tracing Network routing Network allocation
Network Tracing Network tracing finds a particular path through the network based on criteria provided by the user. Example: Finding a path (from a position on the network) which will connect the nearest ATM of SBI bank
Network Routing Point-to-point (source to destination) Point-to-multiple-point (with intermediate stops)
Network Allocation Designation of portions of the network to supply centers or destination points.
SURFACE ANALYSIS
Surface Analysis Common techniques: Deriving contours/isolines Deriving slope Deriving aspect Hillshade analysis Viewshed analysis Watershed analysis Surface intersection
Deriving Contours/Isolines
Deriving Slope
Deriving Slope
Deriving Aspect
Hillshade Analysis DEM Hillshade
Viewshed Analysis
Watershed Analysis
Surface Intersection
GEOSTATISTICS
Geostatistics Geostatistics offers a way of describing the spatial continuity of natural phenomena and provides adaptations of classical regression techniques to take advantage of this continuity. Common techniques: Spatial autocorrelation Interpolation
GEOVISUALIZATION
Geovisualization Geovisualization (short for geographic visualization) refers to techniques and tools designed to interactively visualize spatial phenomena. Common techniques: Classification and reclassification Map comparison Chart Report Layout 3D visualization
Classification
Classification
Reclassification
Reclassification
Reclassification
Reclassification
Reclassification Difference between classification and reclassification
Map Comparison
Chart
Report
Layout
3D Visualization
THANK YOU