DISTORTION PROPERTIES IN MAP PROJECTIONS


Hi all, i read this somewhere and i found it good to share with you, especially my classmates. Hope you'll benefit.


DISTORTION PROPERTIES IN MAP PROJECTIONS
  • angles, areas, directions, shapes and distances become distorted when transformed from a curved surface to a plane
  • all these properties cannot be kept undistorted in a single projection
    • usually the distortion in one property will be kept to a minimum while other properties become very distorted
1. TISSOT'S INDICATRIX
  • is a convenient way of showing distortion
  • imagine a tiny circle drawn on the surface of the globe
  • on the distorted map the circle will become an ellipse, squashed or stretched by the projection
  • the size and shape of the Indicatrix will vary from one part of the map to another
  • we use the Indicatrix to display the distorting effects of projections
2. CONFORMAL (ORTHOMORPHIC)

  • a projection is conformal if the angles in the original features are preserved
    • over small areas the shapes of objects will be preserved
    • preservation of shape does not hold with large regions (i.e. Greenland in Mercator projection)
    • a line drawn with constant orientation (e.g. with respect to north) will be straight on a conformal projection, is termed a rhumb line or loxodrome
  • parallels and meridians cross each other at right angles (note: not all projections with this appearance are conformal)
  • the Tissot Indicatrix is a circle everywhere, but its size varies
  • conformal projections cannot have equal area properties, so some areas are enlarged
    • generally, areas near margins have a larger scale than areas near the center
3. EQUAL AREA (EQUIVALENT)


  • the representation of areas is preserved so that all regions on the projection will be represented in correct relative size
  • equal area maps cannot be conformal, so most earth angles are deformed and shapes are strongly distorted
  • the Indicatrix has the same area everywhere, but is always elliptical, never a circle (except at the standard parallel)
4. EQUIDISTANT


  • cannot make a single projection over which all distances are maintained
  • thus, equidistant projections maintain relative distances from one or two points only
    • i.e., in a conic projection all distances from the center are represented at the same scale


Comments

Post a Comment

Popular posts from this blog

Converting ARCMAP .shp to Adobe Illustrator .AI file

Hello dear Geo-geeks, Its been a while long time since I post geo stuff here, today I would like to take you through on how An ARCGIS .shp file can be converted to .AI file for further Graphic designs. Exporting From ArcGIS to Illustrator Adobe Illustrator is a vector drawing program that accepts files of type .AI. This software can be very useful if you wish to use geometry from GIS as the basis for diagrams that you would create in illustrator, or if you want to use illustrator to fix some of the awkward legends or labels that ArcMap makes for you. TRICKY features of Adobe Illustrator includes; None of your layers can use transparency  If you are using special fonts or spot symbols, they must be converted to polygons in illustrator. There is a limit to the number of vertices that can be exported to illustrator.   Those are the important rules to remember in arcmap document. Setting up your ArcMap Document You may have designed a map in ArcMap wi...
Read more

UTM ZONES IN KENYA

Universal transverse Mercator In Kenya is the mostly used map projection due to its accuracy in conformality hence preserving the shape of the earth. Global Features of utm i)   20 latitudinal belts of 8 deg in the N-S directions labeled from C at 80 degrees South-72 degrees         South to X at 72 degrees North -84 degrees North .     Kenya in belt M and N (ii)  The  origin  of  longitude  is  the  central  meridian.  The  origin  of  latitude  is  the            equator (iii)  False northing is 0 m N but 10,000,000 m S  for southern hemisphere to avoid the          use of negative figures. (iv)  False easting is 500,000 m for each zone (v)  Scale factor at central meridian is 0.9996 (vi)  Latitude varies from 84 degrees north to 80 degrees south The reference ellipsoid used in Kenya is...
Read more

Expanding Geospatial Minds

WELCOME TO GIS WORLD Hello everyone, Its been a while since I posted something here. Today, I want us to look at how one can become a GIS professional from scratch. This actually was triggered by  receiving so many Questions from social media about what Geo-spatial and Remote Sensing as a course is. Well, many of them were freshers who have been placed to various universities to study the course while others just curious about the course and wanted to know if it can be a lifetime profession to consider.  For my case, I never had a glue of what GIS & RS was back in 2014 when i joined the University. Since there were little knowledge about it in Kenya by then unlike now, I never got anyone to guide me if the course was good or not. Then I just applied and boom, I was LUCKY! to get an opportunity to study this new...
Read more