What is GIS?• Any manual or computer based system design to store, analyze, manipulate, display spatially referenced data.• The ultimate purpose of GIS is to answer spatial questions and not necessarily making pretty MAPS!!!• GPS and online maps works on GIS. 2
Spatial Data• Information related to “existing space”.• Since the whole system deals with aspects of our everyday life, it suppose to be updated regularly to keep it current and reliable.• It is made of longitude and latitude. 3
Components of GIS• Hardware & Software – Hardware is a physical device which can be used by the end users like a graphic device or a plotter or scanner. – Software is related to processes to define, store and manipulate the data like a DBMS. – GIS follows 3 tier architecture and still different modules are applied to GIS to provide efficient service.• Data – It is divided in 2 categories: Vector and Raster. 5
Vector: Made up of a dot. Objects are represented by points, lines and polygons.Raster: Made up of pixel. Can be of 2 dimension (pixel of block) or 3 dimension (voxel). It is made up by adding different layers. 6
People People are involved in each part of GIS. That includes cartographers and analyst who who creates the maps and surveys the land. System users who collects the data, upload data to system, manipulate the system and analyze the result.
Characteristics of data in GIS• Location – Location of an object is specified by co ordinates in system – It is shown by point, line or a polygon.• Temporality – A database should record existence and its updated location of an object both. – It is crucial when it is require to find a path in a dynamic fashion like tracking a land parcel.
Thematic Value Different properties and qualities of an object may be represented as attributes.Fuzzy Object Deals with the uncertainty of an object’s location and thematic classification. The location of an object is represented by degree of error. Countries and states are always on a dynamic state of moving boundaries, roads and buildings cause 100% accuracy may not be kept while recording it.Object ID Object should be uniquely identified in the data model in the data model. Eg National Highway 8, Western Express Highway.
Entity v/s field based data The world can be represented as a set of discrete entity such as forests, rivers, roads and buildings which is referred as Entity Based Approach. Field based approach represents world as natural phenomenon like air pollution or may be humidity.Generalization Objects may be aggregated from larger to lower scale while opposite may not be possible. Collection of pixels having 2 Mtr dimensions can be aggregated to generate a pixel of 10 Mtr but 10 Mtr pixel can’t be aggregated to generate a pixel of 2 Mtr. States can be aggregated to generate a country but aggregated countries can’t be aggregated to generate a state, that doesn’t make sense even!
Data Quality Refers to the credibility and accuracy of the data and more generally how good data is. Quantitative quality refers to the measurable components such as spatial accuracy. Qualitative quality refers to the non-measurable components and some specific objects like area of a mountain.
Constraints of GIS• As a part of constraints a GIS database may have primary key, foreign key etc.• A state and country is going to have a capital which can be kept as primary key and one can track the country by selecting a state which can be done with having a foreign key• This constraints are classified in 4 categories. 13
Topological Integrity Constraint: Deals with the behavior of features and the spatial relationship between them. Used during insert and update processes to help reduce errors and improve data quality.Semantic Integrity Constraint: Defines whether the database state is valid according to semantic rules that apply to features. Eg a road declared as ONE WAY or ENTRY RESTRICTED.User-defined Integrity Constraint: Refers to the rules made by humans. Eg. A house should be having a 10 ft distance from a main road.
Temporal Constraint: That are differentiated in punctual and durable temporality. Punctual temporality refers to event with a specific time such as an accident, earthquake, party and so on. Durable temporality refers to the event occur over a period of time like a bridge built and demolished after some years. Generalization is also considered as a constraint some times.
GIS Standards and Operation:• Understand the system requirements.• Standards organizations such as Open Geospatial Consortium(OGC),the U.S. Federal Geographic Data Committee(FGDC),the International Organization for Standardization(ISO).
Methods for testing spatial relationbetween geometry• Equal • Contain• Disjoint • Overlap• Intersect • Relate• Touch• Cross• Within
Example: create table STATES ( StateName varchar(20) primarykey, Shape varchar(20), Country reference COUNTRIES ); Select StateName from STATES where (AREA(Shape)>500000); 19
GIS application and software• Used by specific organization and disciplines such as the military and government• Expanded to real-estate , city planning, navigation,transportation,emergency services,etc.• ArcGIS provided map-making, analysis,data collection,etc.
Future work in GIS• Data Sources• Standards• New Architecture• Mobile GIS• Temporal GIS• Modeling multiple aspect of GIS• Common Notation• Specialized DBMS for GIS