At certain times when loading new layers into ArcMap, a warning message (“The following data sources you added are missing spatial reference information. This data can be drawn in ArcMap, but cannot be projected”). This is because the added layers do not have a coordinate system, probably because, while creating the layers, the spatial reference system was omitted.
It is recommended not to define a coordinate system if you are not sure it is the correct one. To define the coordinate system in a layer (vector or raster) go to the following address:
ArcToolbox > Data Management Tools > Projections and Transformations > Define Projection
In the pop-up window you must configure the parameters described below:
Input Dataset or Feature Class: Select the vector or raster layer.
Coordinate System: Select the coordinate system (Projected Coordinate Systems > UTM > WGS 1984 > Southern Hemisphere > WGS 1984 UTM Zone 17S).