The projection of a map window is specified in the New Map dialog when we create the map. Any layers in the map which use a different coordinate system will be automatically reprojected on the fly into the projection used by the map. That happens so fast, that we can have many layers in the map, all using different coordinate systems, without noticing any delay in panning or zooming caused by the reprojection on the fly into the map's coordinate system.
If desired, we can change the projection used by a map with the Info pane.
See the Coordinate System dialog topic for details on using the dialog.
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 reproject layers on the fly from other projections into the projection used by the map. Manifold is so fast that in almost all cases the process of reprojecting layers on the fly into the projection used by the map will not be noticeable, not even with layers that are tens or even hundreds of gigabytes in size. But with exceptionally big components or with very many large layers displayed within a map that use a different projection than the map, the time required reprojection on the fly might become noticeable, or even unacceptable.
In such cases we will create the map using whatever coordinate system is used by the biggest layer in the map, so there will be no need for reprojection 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 two ways to fix slow rendering in that situation:
Reprojecting the huge component into the projection of the map may be the only good choice if one of the map layers, such as a background web server layer from Bing, is an image that cannot be reprojected without ruining the aesthetic look of the layer. What appear to be labels in imageserver layers, like those from Bing, are really only arrangements of pixels. When reprojected into a different projection from the originally-intended Pseudo-Mercator, the text in the labels will be distorted. That is a consequence of the image-based technology that Bing, Google, and other web server sources have chosen to use.
In such cases the map should use Pseudo-Mercator, just like the web server layer, so that layer is not distorted. Other layers, even very big ones, should be reprojected using Reproject Component into Pseudo-Mercator if the reprojection on the fly for display is not as fast as desired.
Manifold 9 - Re-Project a Shapefile - New coordinate system dialogs make it easier than ever to reproject data, often in only one click. This video shows how to import a shapefile and then rapidly reproject it into different coordinate systems. We then show how maps reproject their contents on the fly for display and how to exploit that to rapidly show data in different projections.
Assign Initial Coordinate System
Base Coordinate System
Favorite Coordinate Systems
Favorite Base Coordinate Systems
Example: Convert a 0 to 360 Degree Projection - We often encounter data, both images and drawings, using latitude and longitude degrees that appears to be in Latitude / Longitude projection but which has longitude values from 0 degrees to 360 degrees and latitude values from 0 degrees to 180 degrees, instead of the usual arrangement of -180 degrees to 180 degrees for longitude centered on the Prime Meridian, and -90 degrees to 90 degrees for latitude centered on the Equator. This example shows how to utilize such data by assigning the correct projection.
Example: Import Shapefile and Create a Map - Step by step process to import a shapefile and to create a map.
Example: Import a Shapefile - ESRI shapefiles are a very popular format for publishing GIS and other spatial data. Unfortunately, shapefiles often will not specify what projection should be used. This example shows how to deal with that quickly and easily.
Example: Reproject a Drawing - An essential example on changing the projection of a drawing, either within the drawing itself, or by changing the projection of a map window that shows the drawing and on the fly reprojects the drawing for display.
Example: Assign Initial Coordinate System - Use the Info 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 Reproject Component 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.
Reprojection Creates a New Image - Why changing the projection of an image creates a new image.
About Coordinate Systems