Coordinate systems of type latlon are suitable to store data, for display and/or printing purposes (map view and layout), it is advised to use a coordinate system of type projection in a map window. In ILWIS 3, object names comply with Windows long file names. Also Universal Naming Convention (UNC) paths are supported. For more information, see How to use long object names. To create a coordinate system, you can select the Create Coordinate System command on the File menu of the Main window or double-click the NewCrdSys item in the Operation-list. The Create Coordinate System dialog box will appear: you can create any type of coordinate system. The easiest way to view and/or edit an existing coordinate system, is to double-click a coordinate system in the Catalog. When one or more raster and/or vector maps are displayed in a map window, you can also open the Edit menu in the map window and choose Coordinate System. A coordinate system consists of an ASCII object definition file (.CSY), in case of a coordsys tiepoints also a binary data file (.CS#) is available. The object definition file stores the coordinate boundaries and, if available, projection information, a formula, etc. A projection defines the relation between the map coordinates (X,Y) and the geographic coordinates latitude and longitude (f, l). Based on the shape of the projection surface, one can classify the projections in azimuthal, conical and cylindrical projections. Therefore, the cone or cylinder needs to be ‘unrolled’ to form a plane map. Cylindrical projections may be imagined as the projection to a plane that is wrapped around the globe in the form of a cylinder (see Figure 1). After unrolling, the outline of the world map would be rectangular in shape, the meridians are parallel straight lines which cross at right angles by straight parallel lines of latitude. Together, these lines are called the ‘graticule’. Examples: Mercator, Plate Carree. Azimuthal projections may be imagined as the projection on a plane tangent to the globe (Figure 2). The characteristic outline of the world map would be circular. If the pole is the central point, the meridians are straight lines, spaced at their true angles intersecting at this center point. Parallels are represented as concentric circles. Examples: Gnomonic, Stereographic. Conical projections may be imagined as the projection to a plane that is wrapped like a cone around the globe (Figure 3). After unrolling the outline of the world would be fan shaped. The meridians are represented as straight lines and parallels as concentric circles. Only the parallels where the cone touches the globe have the same length as on earth. Furthermore, projections can be subdivided according to the direction in which a cylinder, plane or cone is oriented with respect to the globe, the so-called aspect. In the text above, it is assumed that the projection only touches the Earth. However, it is also possible to use a secant cylinder, plane or cone which intersects the sphere. Figures 4, 5, and 6 show some aspect types for different types of projections. As mentioned before a map projection always results in some deformation or distortion. Depending on the type of projection, these distortions will be different. This is indicated by the characteristics of a projection: Map projections are named according to the class, the aspect, the property, the name of the originator and the nature of any modification. For an overview of available projections, refer to the Select Projection dialog box. For hints on what projection to use, refer to Suggested projections. You can create a coordinate system formula for maps with artificial coordinates, i.e. starting at (0,0) or digitized in millimeters. The coordinate system formula uses a ‘related’ coordinate system, this is the coordinate system with correct coordinates. When you have defined the formula and when the map with artificial coordinates uses the newly created coordinate system formula, then you can transform the map to the correct coordinate system. In the formulae below, is used for the related coordinates, for the coordinates of the coordsys formula which you are creating, for the origin in the related coordsys, and for the origin of the coordsys formula which you are creating. Source.