Lecture 4: Georeferencing. Thanks to Joana Barros: Birkbeck College, London. Georeferencing. ‘To georeference’ the act of assigning locations to atoms of information Is essential in GIS, since all information must be linked to the Earth’s surface The method of georeferencing must be:
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
Thanks to Joana Barros: Birkbeck College, London
E.g. distance from the Equator or from the Greenwich Meridian
Forward Sortation Areas (FSA)
The first three characters of the six-character postcode form the FSA
Central part of the Toronto metropolitan region
ZIP code boundaries are a convenient way to summarize data in the US. The dots on the left have been summarized as a density per square mile on the right
Latitude: is the angular distance, in degrees, minutes, and seconds of a point north or south of the Equator. Lines of latitude are often referred to as parallels.
Longitude: is the angular distance, in degrees, minutes, and seconds, of a point east or west of the Prime (Greenwich) Meridian. Lines of longitude are often referred to as meridians.
The Earth more accurately modeled as an spheroid (ellipsoid) than a sphere
An spheroid is formed by rotating an ellipse about its shorter axis
Ellipsoid allows variable radiiThe Earth’s shape
But many technologies for working with geographic data are inherently flat (Cartesian)!
Both types of projections will generally distort distances
The Lambert Conformal Conic projection is commonly used to map North America
On this projection lines of latitude appear as arcs of circles, and lines of longitude are straight lines radiating from the North Pole
Conceptualized as the result of wrapping a cone of paper around the EarthConic Projections
Is neither conformal nor equal area
As latitude increases, lines of longitude are much closer together on the Earth, but are the same distance apart on the projection
Assign latitude to the y axis and longitude to the x axis
Also known as the Plate Carrée or Cylindrical Equidistant ProjectionThe “Unprojected” Projection
Implemented as an internationally standard coordinate system
Initially devised as a military standard
Uses a system of 60 zones
Maximum distortion is 0.04%
Transverse Mercator because the cylinder is wrapped around the Poles, not the EquatorThe Universal Transverse Mercator (UTM) Projection
Zones are each six degrees of longitude, numbered as shown at the top, from W to E
Earth is continuously circled by 24 GPS satellites
A GPS receiver listens for signals which give the satellites’ location and the exact time of sending.
Trilateration then gives them your latitude, longitude