Shipwreck Databases Western Australian Museum

ArcView How to do it Manual No. 2: Georeferencing CAD Files

Author/s J.N. Green

Year of publication 2007

Report Number: 227

What is georeferencing?
A Geographical Information Systems (GIS) is a system for creating, storing, analysing and managing spatial data and associated attributes. In a GIS a variety of graphical information can be displayed in form that allows the geographical coordinates of a particular point to be determined. Georeferencing is the process of scaling, rotating, translating and deskewing graphical information, raster or vector images, to match the geographical coordinate system (previous How to document ahs dealt with raster images).

An ordinary raster image is made up of pixels that have no particular size. A vector image is made up of equations hat define lines and areas. In general, vector images are smaller and much easier to scale. A vector image as it is magnified maintains its shape and does not pixilate like a raster image. Unlike a raster image which when it is georeferenced, each individual pixel is give a particular coordinate corresponding to the point on the ground that it represents; a vector image generally only needs two coordinates to locate its position.

What can you georeference?
A vector image cannot be georeferenced using the georeferencing tool in ArcMap. It is necessary to either project the Vector file or build a world file do that the CAD is displayed in its correct orientation. All image files used here are available on a CD or on the server for you to play with.