WHAT IS THE DATA
Data are units of information. The data are collected through observation. Data are used in scientific research, engineering, surveying, transport, business management, finance, governance, etc. The Data are measured, collected, reported, and analyzed. The data are visualizations and produced such as graphs, tables, and images. In the GIS the data stored information about the world. In the GIS the data are collected through thematic layers and linked with the geographical information system.
There are two types of basic data using in the GIS.
1. Spatial Data.
2.Attribute Data.
1. Spatial Data:- Spatial data describe as which has the absolute and relative location of a geographic feature on the earth's surface. In the GIS spatial data has physical dimensions on the earth. The spatial data explained in the form of point, line, area, and surface on a map. The spatial data explain in tabular form, a geographical map, a digital map, and a remotely sensed map. The spatial data are stored in a graphic file and managed by the file management system
. The spatial data are represented in two basic models in the GIS.
. The spatial data are represented in two basic models in the GIS.
(i) Vector Data Model
(ii)Raster Data model
(i)Vector Data Model:- In the vector data model location of geographic feature is stored in the form of vectors or dimensional lines. All vertex of the geographic feature has ( x,y) coordinates or longitude and latitude.
One pair coordinates and vertex represent a point feature. The polygon feature contains no. of closed coordinate pair and vertices. Vector lines are consist of a string.
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| Vector data map |
(ii) Raster Data Model:-Raster data model is defined as the model that incorporates the use of grid cell.
In the raster model data of geographical area is divided into row and column. The size of a cell depends on the tessellated data structure based on the data accuracy and the resolution needed.
point raster
polyline raster
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| polygon raster |
2.Attribute Data:-Attribute data is used in GIS for describing the map features. Any geospatial data has three major components such as position, attributes, and time. The attributes data are linked with spatial data or geometric data.
The storage and management of GIS data are four models.
(I) Tabular:- In the tabular model the data are stored in sequential data files with fixed formates.In this model the location attribute values in a predefined record structure. It has limited indexing capability for records.
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| TABULAR MODEL |
(II) Hierarchical Model:-The hierarchical dataset organizes data in a tree structure. Data is structured downward in the hierarchy of tables. Any level in the hierarchy can have unlimited children. But any child can have only one parent. A hierarchical model is a tree structure. The advantage of the hierarchical model has a high-speed dataset and ease of updating.
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| Hierarchical Model |
(III) Network Model:-The network database organizes data in a network. The network DBMS have not much more acceptance in GIS than the hierarchical DBMS. The more powerful structure for representing data relationships allows for more realistic modeling of geographic phenomena.
(IV) Relational Model:-The relational database organizes the data in the table form. Each table is identified by a unique table name, and it is organized by rows and columns. Each column within a table also has a unique name. There are many different DBMS designs, but the relational design has been the most useful in a GIS. In the relational design, data are stored conceptually as a collection of tables. Common fields in different tables are used to link them together.
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