**ET GeoWizards and
Projections**

**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 - 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 - 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 feature classes the projection information is
stored in the feature classname.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 feature classes - "feature classname.prj") is missing

**Projections of the dataframe (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.

**ET GeoWizards works with data in any projection and view frame in any
projection**

**Notes:**

- All the wizards preserve the Spatial Reference of the input data source. The assumption is that if the user keeps a dataset in certain projection he has reasons for that, and all the products of this data set must be in the same projection.
- When a distance input is required ( Fuzzy tolerance, Dangling tolerance etc. ) best results will be achieved if the data is projected in a specific projection and the data frame does not have projection (or has the same projection as the data), because the tolerance is compared directly with the data.
- The Wizards will not work if the data frame contains one or more layers that have projection with Geographic Coordinate System different from the Geographic Coordinate System of the data frame's projection. ArcMap gives a warning in such a case, but allows it.
- Although possible, it is not recommended to manipulate Unprojected data (data in a Geographic Coordinate System) for reasons mentioned above
- If the projection information is missing, the data can be manipulated only in a data frame with no projection assigned.

Copyright © Ianko Tchoukanski |