Open Table of Contents

Some short definitions (compiled from ArcGIS desktop help)

• Projection - The two-dimensional representation of the three-dimensional space.
• Coordinate System - a reference system for measurements defined by the projection
  • Geographic Coordinate System (GCS)   - measures locations in degrees - latitude and longitude. Since latitude and longitude are angular measurements they are not suitable for measuring distances. The major parameter of a Geographic Coordinate System is its datum
  • Projected Coordinate System (PCS) - uses a projection to transform the latitude and longitude to X and Y coordinates and makes the linear measurements more accurate. Each projected coordinate system is based on a Geographic Coordinate System
• Spatial Domain -  the range and precision of coordinates that can be stored in a feature dataset
• Spatial Reference - contains information for the coordinate system and spatial domain extent for a feature dataset

Projections of the data ( for shapefiles the projection information is stored in the shapefilename.prj file)

• Projected data - the data is explicitly projected in a Projected Coordinate System
• Unprojected data  - the data is in a Geographic Coordinate System
• Data with unknown projection - the projection information ( in the case of shapefiles - "shapefilename.prj") is missing

Projections of the data frame (View)

• No projection - the data is displayed as is
• Assigned projection - the data is reprojected on the fly and displayed in the data frame's projection.

Important notes:

• It is strongly recommended the projections of the edited layer and the data frame (the view) are the same when editing.
• The functions of ET GeoTools check the projections of the data frame and the edited layer and if different project on the fly between the two therefore all the tools  will work if the spatial reference of the edited layer is different from the one of the data frame
• If the geographic coordinate systems of the spatial references of the edited layer and the data frame are different the attempt to project the shapes between the two might fail - NEVER edit data in a data frame that has different GCS from the layer to be edited

Copyright © Ianko Tchoukanski