Map Projection

The projection of a map window is automatically set by whatever is the first component added to the map window.  Drag and drop a drawing that uses Lambert Conformal Conic projection into a map window as the first layer added to the map and the map window will immediately configure itself to use Lambert Conformal Conic projection.   Components added to the map thereafter will be automatically re-projected on the fly into the projection used by the map if the component uses some projection other than the projection used by the map.  

 

If desired, we can change the projection used by a map with the Edit - Map Projection dialog.

 

To change the projection used by a map:

 

  1. Open the map.
  2. Choose Edit - Map Projection in the main menu.
  3. That launches the Coordinate System dialog.  Use the dialog to choose a new coordinate system and press OK.

 

See the Coordinate System dialog topic for details on using the dialog.

 

Notes

Synonyms -  The terms projection and coordinate system are used as interchangeable synonyms in Manifold.  Cartographers favor the term projection while programmers seem to prefer coordinate system.  This documentation uses the two terms interchangeably, with the term projection tending to be used more in GIS or display contexts and the term coordinate system tending to be used more when discussing programming, SQL or standards.

 

Convenience vs. Speed - It is very convenient that maps will re-project layers on the fly from other projections into the projection used by the map.   But that can be slow in the case of huge components displayed within a map that use a different projection than the map.   It takes time for the re-projection process to occur, possibly an annoying amount of time for a big component.  

 

If we are thinking ahead we will create the map and then make sure that the first component we add to the map is the biggest one it will show, so that there is no need for re-projection on the fly for the biggest component that will be displayed in the map.   Sometimes, however, we might forget, creating the map and adding a very small component, and then only later adding to the map some huge component in a different projection.   There are three ways to fix slow rendering in that situation:

 

 

 

 

See Also

Coordinates

 

Projections

 

Change Projection

 

Initial Projection

 

Coordinate System

 

Base Coordinate System

 

Favorite Coordinate Systems

 

Favorite Base Coordinate Systems

 

Example: Assign Initial Coordinate System - Use the Contents pane to manually assign an initial coordinate system when importing from a format that does not specify the coordinate system.

 

Example: Change Projection of an Image - Use the Change Coordinate System command to change the projection of an image, raster data showing terrain elevations in a region of Florida, from Latitude / Longitude to Orthographic centered on Florida.

 

Example: Adding a Favorite Coordinate System - Step by step example showing how to add a frequently used coordinate system to the Favorites system.

 

Example: Detecting and Correcting a Wrong Projection - A lengthy example exploring projection dialogs and a classic projection problem.  We save a drawing into projected shapefiles and then show on import how a projection can be quickly and easily checked and corrected if it is wrong.

 

Re-Projection Creates a New Image - Why changing the projection of an image creates a new image.

 

About Coordinate Systems

 

Projections Tutorial