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Introduction to GIS
- 1. Introduction to GIS MayureshPadalkar 09-10-2017 1
- 2. Agenda • GIS andits uses • Softwares • Data - Vector and Raster • Projection 209-10-2017
- 3. What is GIS? •GIS is a system designed to capture, store, manipulate, analyze, manage and present spatial or geographic data • GIS can relate unrelated information by using location as the key index variable • History: The first known use of the term GIS was by Roger Tomlinson in the year 1968 in his paper "A Geographic Information System for Regional Planning". Tomlinson is also acknowledged as the “Father of GIS” 09-10-2017 3
- 4. Uses of GIS •GIS can refer to a number of different technologies, processes and methods. • Applications related to engineering, planning, management, transport/logistics, insurance, telecommunications and business. 09-10-2017 4
- 5. Which software? • QGIS,MapInfo, ArcGIS, Global Mapper, Erdas, gVSIG, GRASS, SAGA, etc. • What suits best for me? 09-10-2017 5
- 6. GIS data • Datais nothing but information • The longitude and latitude columns hold geographical data and rest is non- geographical data. • Data: Vector and Raster 09-10-2017 6
- 7. Vector Data • Itis stored as a series of X, Y coordinate pairs inside the computer’s memory i.e. shp, tab, etc. through integer, float and string • It is used to represent points, lines (polylines) and areas (polygons) i.e. features • It is a shape represented using geometry which consists various vertices i.e. digitising • Information is stored in attributes i.e. tables • Depends on what you want to represent!! i.e. scale and convenience 09-10-2017 7
- 8. Raster Data • Itis stored as a grid of values i.e. matrix of cells, pixels which define the spatial resolution • There are many satellites circling the earth and the photographs they take are a kind of raster data that can be viewed in a GIS i.e. real world data • Important difference between raster and vector data is that if you zoom in too much on a raster image, it will start to appear ‘blocky’ • Generally used as a backdrop along with vector 09-10-2017 8
- 9. Georeferencing • It isthe process of defining exactly where on the earth’s surface an image or raster dataset was created • This positional information is stored with the digital version of the aerial photo • When the GIS application opens the photo, it uses the positional information to ensure that the photo appears in the correct place on the map • The georeferencing information for a raster is often provided in a small text file accompanying the raster 09-10-2017 9
- 10. Sources of rasterdata • Aerial photography and Satellite imagery • Raster data can be computed eg. dMax • From vector data 09-10-2017 10
- 11. Difference between Vector& Raster Vector • Point, polyline and polygon • Information is available as attributes • Size is less • Clearly visible i.e. quality is retained • Formats: shp, tab, dxf, kml, csv, etc. Raster • Pixels or cells • Only in a single cell • Sometimes consumes very large disk space • Depends upon zooming • ASCII, GeoTIFF, bmp, jpeg, pdf, Virtual Raster, grid, etc. 09-10-2017 11
- 12. Conversion between Rasterand Vector • Raster to Vector: Possible but requires high end tools to identify the same bandwidth and processing eg. roads, buildings, etc. • Vector to Raster: Easy but generally useful to non-GIS users and attribute information is lost 09-10-2017 12
- 13. Projection • Where amI? • Most commonly used: Longitude and Latitude • Map projections try to portray the surface of the earth or a portion of the earth on a flat piece of paper or computer screen • A CRS then defines, with the help of coordinates, how the two-dimensional, projected map in your GIS is related to real places on the earth • Deciding factor while starting any project/work 09-10-2017 13
- 14. Map Projection • Theprocess of creating map projections can be visualised by positioning a light source inside a transparent globe on which opaque earth features are placed • It is not an exact representation of the spherical earth i.e. distortions of angular conformity, distance and area • 3 families 09-10-2017 14
- 15. Co-ordinate Reference System •Every place on the earth can be specified by a set of three numbers, called coordinates • CRS can be divided into projected CRS (aka Cartesian or rectangular CRS) and geographic CRS 09-10-2017 15
- 16. Geographic CRS • Theuse of Geographic Coordinate Reference Systems is very common • They use degrees of latitude and longitude and sometimes also a height value to describe a location on the earth’s surface • The most popular is called WGS 84 • Lines of latitude run parallel to the equator and divide the earth into 180 equally spaced sections from North to South • Each hemisphere is divided into ninety sections • In the northern hemisphere, degrees of latitude are measured from zero at the equator to ninety at the north pole • Lines of longitude run perpendicular to the equator and converge at the poles • The reference line for longitude (the prime meridian) runs from the North pole to the South pole through Greenwich, England • Lines of longitude are measured from zero to 180 degrees East or West of the prime meridian • West of the prime meridian are assigned negative values 09-10-2017 16
- 17. Projected CRS • A2D CRS is commonly defined by two axes. At right angles to each other, they form a so called XY-plane while in 3D CRS, Z is added • Every point that is expressed in spherical coordinates can be expressed as an X Y Z coordinate • UTM is often used – global map projection divided into 60 zones • The position of a coordinate in UTM south of the equator must be indicated with the zone number (35) and with its northing (y) value and easting (x) value in meters 09-10-2017 17
- 18. Summary • Understanding aboutGIS • Which software should I work on? • What am I working on? • Understanding about projection 1809-10-2017
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