Georeferencing is a very important topic for both GIScientists and GISystem specialists. It is the means by which data from different sources can be integrated; without georeferencing GIS never would have been developed (as mentioned in the 2nd lecture: Geography integrates data). Furthermore, one of the more common sources of avoidable error in spatial analysis can be traced back to an improper understanding of georeferencing--using data that are referenced to different datums, selecting an incorrect map projection, etc.  Luckily there are many sites devoted to georeferencing, so one can quickly become familiar with all of the different topics included within the framework of georeferencing. The principle topics that are usually included within an discussion on georeferencing are:

• Geodesy
• Map projections
• Coordinate Systems

Fundamental to understanding map projections is first understanding how the earth itself is described--this involves understanding geodesy. The Federal Government has produced some educational materials related to geodesy and they provide a historical perspective on our views of the earth over time. Datums are the link between geodesy and map projections--on the Geographer's Craft site you'll find detailed notes that describe geodetic datums and map projections. From a GIS perspective, coordinate systems follow from projections--each coordinate system is linked to a particular datum--map projection combination (what I refer to as a Projection-based coordinate system). The Australian Surveying and Land Information Group have developed some wonderful materials--check out the section on Earth Monitoring and Reference Systems, and the subsections therein. You'll find a good discussion on datums and coordinates. Wiley (a textbook publisher) has made available selected chapters from the 1991 "Big Book" of GIS--chapter 10, by D. H. Maling, on Coordinate systems and map projections for GIS is well worth reviewing for those wishing to get a thorough overview of the subject. Paul Cote at Harvard has prepared these useful notes on Coordinate Systems (worth reviewing), and these notes on Rectangular Coordinate Systems (the topics covered include rubber sheet transformations). A useful set of pages related to coordinate systems and more has been provided by the Wisconsin State Cartographers Office.

Some other useful sites include this page that describes describes the Universal Transverse Mercator projection and its relation to grids, this PDF which describes datum shifts and how that affects the coordinates shown on a topo map, this page which describes how to use UTM coordinates with a GPS, and this one which describes the need to convert map-based measurements (UTM) to actual ground measurements. (Unfortunately, the formula used to convert the measurements is not fully described in the paper). You should be aware that there are significant changes when converting distances from a UTM map to the equivalent ground distance when using NAD27 and using NAD83 (this figure illustrates the issues).

Some NCGIA notes contain useful material:

Show links to the notes Hide links to the notes

The BC Ministry of the Environment has produced some brief notes on projections. One note describes the BC Environment Standard Projection (the "official" map projection for maps of BC), and another (now gone, so I have posted a copy of the note) provided a brief tutorial on map projections.

Some figures that illustrate some map projection concepts can be found here. For a picture gallery of map projections in their normal, transverse and oblique aspects, check out the Differential Geometry and Geometric Structures pages. I have created a simple figure to illustrate the basis upon which the Great Circle distance calculation is derived. Here is a figure that illustrates the concept of a false origin, and one that illustrates the differences between distances as measured on a grid, the ellipsoid, the geoid and on the ground.  The City of Coquitlam's Engineering Department describes how they use linear referencing (PDF).

Learning objectives

• Know the requirements for an effective system of georeferencing;
• To become familiar with the problems associated with placenames, street addresses,
  and other georeferencing systems used every day by humans;
• Recognized how the Earth is measured and modeled for the purposes of positioning;
• Become familiar with the basic principles of map projections, and the details of some
  commonly used projections;
• Understand the importance of the need to transform between different systems of georeferencing.

Text: Chapter 5 Georeferencing [Overheads: 1 per page; 3 per page] Movies: geoid, plane-sphere, graticule

Keywords: PBCS, UTM, Projection parameters (surface orientation [normal, transverse], form [plane, conic, cylindrical], contact [tangential, secant]), Geoid, Ellipsoid, (Ellipse) Datum (NAD27, NAD83), cadastre, WGS84 vs GRS80

A definition of metric: met·ric2 (mtrk) ETYMOLOGY: Greek, (the art) of meter, feminine of metrikos, relating to measurement.
n.
A standard of measurement.
Mathematics. A geometric function that describes the distances between pairs of points in a space.