Projection, Scale, Accuracy and Resolution (the key properties of spatial data))

Projection: the method by which the curved 3-D surface of the earth is represented by X,Y coordinates on a 2-D flat map/screen

• distortion is inevitable

Scale: the ratio of distance on a map to the equivalent distance on the ground

• in theory GIS is scale independent but in practice there is an implicit range of scales for data output in any project

Accuracy: how well does the database info match  the real world

• Positional: how close are features to their real world location
• Consistency: do feature characteristics in database match those in real world

                               is  a road in the database a road in the real world?

• Completeness: are all real world instances of features present in the database?

                                 Are all roads included.

Resolution: the size of the smallest feature able to be recognized

                            for raster data, it is the pixel size