Sources of Spatial Data

 From where I get spatial data?

        GIS usually handles two types of data, i.e., spatial and attribute data. Data that is connected to a location on Earth's surface is called spatial data. For eg, if I ask a question, "Where is Taj Mahal located?" the probable answer will be "it is in Agra" or "it is located on the banks of River Yamuna", or it is located at 27° 10’ 30.11’’ N latitude and 78° 02’ 31.66” E longitude. The first two answers are examples of  relative location, whereas the last one is an example of absolute location. Location is essential in a geographic information system and are the basis for mapping and linking different kinds of information. Attribute data on the other hand is the description about the spatial data. It is also known as non-spatial data. Various sources of spatial and attribute data are available over the internet. These sources can be broadly grouped into grouped into raster data sources and vector data sources.

Raster Data Sources

    The most common raster images are orthophotos and satellite images. The orthophoto is actually a scanned photographic product. It is geometrically corrected and can be utilized as a map. The satellite image, on the other hand, is obtained electronically and are wholly digital products. Though a number of data sources are available in public domain over the internet, few are listed here (you can directly go to the site by clicking the link below).

USGS Earth Explorer - provides satellite images, aerial photos, digital elevation products and Landsat surface reflectance data.

Alaska Satellite Facility - provides synthetic aperture radar (SAR) datasets and Advanced Land Observing Satellite (ALOS) data.

Earth Resources Observation and Science Center - The largest civilian collection of images of the Earth’s land surface in existence, including tens of millions of satellite images.

National Centers for Environmental Information - Provides ocean and weather datasets. 

USDA Geospatial Data Gateway - provides access to high resolution vector and raster Geospatial Data of environment and natural resources.

Bhuvan Geoportal - providing visualization services and Earth observation data.

Vector Data Sources

Few vector data sources where spatial data are available in public domain are listed below (you can directly go to the site by clicking the link below).
Natural Earth Data - map dataset available at 1:10m, 1:50m, and 1:110 million scales.
DIVA GIS - Data of any country in the world especially administrative boundaries, roads, railroads, altitude, land cover, and population density.
OPENDEM - Portal for sharing open digital elevation data.
IGIS Map - Boundary shapefiles of  Indian states  and assembly constituencies. 

Attribute Data Sources

Attribute data are stored in tables and each row of a table represents a map feature. The sources of attribute data are given below (you can directly go to the site by clicking the link below).
Census of India 
Ministry of Statistics and Programme Implementation
NITI Aayog

In the next post We shall discuss on the topic how to work with data in QGIS.


 

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