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====== GIS Editor Lesson 10: Reprojection ======

===== Map Projection =====

Map projections are tools that allow you to change your map for more precise and accurate representation.  Changing the Map Projection allows you to control the way in which your map data is displayed on your screen.  Projection is a method of representing a spherical body (such as the Earth) on a two-dimensional surface (such as a computer screen). There are many different projections available, each of which represents the spherical curves of Earth in different ways.  The editor comes with four common projections as well as a multitude of others.  The four most common are:

•	**Geographic (Latitude/Longitude)** - also known as WGS84 or EPSG:4326, this projection is commonly used by GPS satellite navigation and by NATO for geodetic surveying. It is the default projection for new maps in the GIS Editor.

•	**Google Maps / Bing Maps / OpenStreetMap** - also known as Spherical Mercator or Web Mercator, this is the projection used by most online web map services.  You will most likely need to use this projection if you want to overlay your layer data on top of a base map from one of the aforementioned providers.

•	**State Plane** - a set of 124 geographic zones designed for specific local regions of the United States. 

•	 **UTM** - a set of 60 geographic zones covering the entire Earth, each of which consists of a six-degree band of longitude.  
Other Projections


If you need to use a projection that is not available on the Common Projections tab, switching to the Other Projections tab will open up a wider range of options for you.

•	**EPSG Search** - allows you to find a projection according to its EPSG number or description. This list has some partial overlap with the ESRI search.

•	**ESRI Search** - allows you to find a projection according to its ESRI number or description. This list has some partial overlap with the EPSG search.

•	**Custom** - allows you to load a custom .prj file which describes the projection for your data. For more information about .prj files. Alternatively, when the Custom option is selected, you can also paste the Proj4 projection string for your intended projection into the Projection String text box at the bottom of the dialog.


Because every projection distorts the data in some areas to a certain degree, choosing the right projection for the maps you want to view is important.  For example, if you will be creating maps of a very specific local region of the United States, you might want to use a State Plane projection which focuses on that region. This will minimize distortion of the region you are working in at the expense of distorting other areas of the world.  Because you will not need to display those other areas of the world, the distortion there is acceptable.

The GIS Editor supports just about any projection imaginable, and makes the most common projections easy to access via the map's Projection Configuration dialog.  For more information about the concept of projecting map data, [[https://en.wikipedia.org/wiki/Map_projection|see here]].

There are also other projections found online, or if you wish to upload your own.  In our lesson today, we will change our projection to view how it changes the map to better display our data. 


===== Changing Map Projection =====
To change the projections locate the “Map Projection” button on the home tab in the ribbon.  Once you click the button a dialog box will be presented that looks like:

{{wiki:Map Projection.png?480}}

From here, you are able to set your map to any projection you wish.  In the GIS Editor, your map will reproject all of your layer data if necessary, no matter what projection it is in, to the projection you specify.  This way, you can load layers whose data are formatted in a variety of different coordinate systems and project them all on-the-fly into a single unified projection of your choosing.

We will want to set ours to Spherical/Mercator, or the Google Maps option.  For learning purposes add a second map to your project and change that map projections to another option.  As you switch back and forth from Map 1 and Map 2, you will notice how the map changes depending on which projection you chose.  

For more Information on Map Projection go [[:Map Projection|here]].

Continue to:
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[[GIS Editor Lesson 11: Getting Your Maps Ready for Presentation]]

Or return to the [[:Introduction to the Map Suite GIS Editor|index of all lessons]].
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