This presentation gives a basic idea of GIS and its uses and different softwares commonly used. It also covers difference between vector and raster. General idea of projection is also covered.

1. Introduction to GIS
Mayuresh Padalkar
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2. Agenda
• GIS and its uses
• Softwares
• Data - Vector and Raster
• Projection
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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”
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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.
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5. Which software?
• QGIS, MapInfo, ArcGIS,
Global Mapper, Erdas, gVSIG,
GRASS, SAGA, etc.
• What suits best for me?
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6. GIS data
• Data is nothing but information
• The longitude and latitude columns hold
geographical data and rest is non-
geographical data.
• Data: Vector and Raster
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7. Vector Data
• It is 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
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8. Raster Data
• It is 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
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9. Georeferencing
• It is the 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
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10. Sources of raster data
• Aerial photography and Satellite imagery
• Raster data can be computed eg. dMax
• From vector data
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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.
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12. Conversion between Raster and
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
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13. Projection
• Where am I?
• 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
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14. Map Projection
• The process 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
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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
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16. Geographic CRS
• The use 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
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17. Projected CRS
• A 2D 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
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18. Summary
• Understanding about GIS
• Which software should I work on?
• What am I working on?
• Understanding about projection
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19. Thank You!!!
Any questions???
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