How it works
VOAProp is a graphical shell, which runs the prediction tools of VOACAP. VOAProp simply creates input files for VOACAP, and then displays the resulting output. If there is any inaccuracy in the results, then it is either in the input file generated for VOACAP, or in VOACAP itself. In either case, the results may be verified by running the appropriate VOACAP program.
Global propagation maps
The global propagation maps provide a way to produce maps similar to those that can be produced using the VOACAP program areawin.exe. To verify the output from VOAProp, or to produce maps where you have control over more of the input data to the propagation model, you can run this program and input the data yourself.
When you select a band tab and change the input values for the map display, VOAProp generates an input file for VOACAP in the folder <voacap_path>\areadata\VOAProp\voaprop.voa . VOACAP itself is then run, which produces an output file <voacap_path>\areadata\VOAProp\voaprop.vg1. VOAProp reads in this file and displays the output, using the DBU column to obtain the signal strengths at each location.
Point to point propagation charts
The propagation charts showing propagation throughout the day between your home location and the selected DX location are a way to produce charts similar to those that can be produced using the VOACAP program pointwin.exe. To verify the output from VOAProp, or to produce charts where you have control over more of the input data to the propagation model, or can view other outputs (such as SNR) you can run this program and input the data yourself.
When you display a propagation chart or change parameters that would affect it, VOAProp generates an input file for VOACAP in the folder <voacap_path>\run\voacapx.dat. VOACAP itself is then run, which produces an output file <voacap_path>\run\voacapx.out. This is read in and plotted as a chart. The propagation predictions are calculated for multiples of 2MHz. Because VOACAP does not allow enough input data to calculate the whole 2 - 30MHz range in one go, the parameters are generated and VOACAP is run twice. Thus if you look in the folder given, you will only ever see the output from the last of the two runs, for the range 2 - 22MHz.
VOAProp uses the VOACAP method 22 for short path predictions, and 21 for long path. If you find that the chart seems to show better propagation when long path is selected, you probably have version 1.0 Release 1 of the software.
VOACAP propagation model
For more information about the VOACAP propagation model itself, see this site.