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.
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're 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, which is described below. For more information about the concept of projecting map data, we recommend this Wikipedia article.
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.
By default, new maps in the GIS Editor use the Geographic (Latitude/Longitude) projection, also known as WGS84 or EPSG:4326. To view or change the current projection of your map, click the Map Projection button on the Home tab of the GIS Editor's ribbon bar. This will bring up the Projection Configuration dialog.
The Projection Configuration dialog consists of two tabs:
If you want to change the projection of your map, you will use either the Common Projections tab or the Other Projections tab to set the projection you want. The most common projections that users will want to access most often can be easily chosen from the Common Projections tab. If you are using a very specific local projection, an obscure projection or a custom projection for which you have a .prj file or a Proj4 string, you will want to use the Other Projections tab.
The GIS Editor provides easy access to a variety of common projections through this tab. Those projections include:
These projections are made available via a series of easy-to-use dropdown menus. Some projections require you to set various options including Datum, Zone and Unit, while others (such as Geographic and Google Maps) do not require any further options to be set.
As you make your selections, the GIS Editor will automatically generate the Proj4 projection string that corresponds to the common projection that you have selected. This string is displayed in a read-only text area beneath the dropdown menus. You will most likely not need to refer to the Proj4 information; though it is particularly useful for software developers who are programming against ThinkGeo's Map Suite GIS components.
Click the OK button at the bottom of the dialog to apply the projection you have chosen.
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.
Click the OK button at the bottom of the dialog to apply the projection you have chosen.
Each layer you load onto your map has an internal projection which is separate from your map's projection. The internal projection identifies the coordinate system in which that layer's data has been stored. The internal projection must be set properly, otherwise the layer data will display in the wrong place on your map (or may not appear at all).
Loading a layer with an improperly-set or unknown internal projection is uncommon, but does happen. This typically only occurs if you have layer data that has been stored in an obscure coordinate system, or if the layer's projection was set incorrectly by mistake.
If you know the true projection of the layer, you can correct this problem by right-clicking on the layer in the Layer List and choosing Layer Projection. This will open the same Projection Configuration dialog we have discussed above, with the difference being that this time you are setting the internal projection in which that specific layer's data is stored.
Please use caution when setting a layer's internal projection, as setting this value incorrectly can cause the layer to display in the wrong place on your map or not at all.
If you are unsure what projection you should use, spatialreference.org is a good resource for finding spatial references in a variety of formats.