The analysis of the published composition – scalar property diagrams of ternary mixtures containing an ionic liquid was performed. Insufficiency of composition – property data for ternary mixtures, especially for different conditions, and the absence of results of the statistical analysis of measurements in the original papers was noted. The main problems that arise when building diagrams of isolines of properties according to the data of the calculation experiment were found. It is shown that in some cases it is fundamentally impossible to simulate the scalar quantities of ternary mixtures using data on binary components, because the boundary contour of the concentration triangle characterized by a certain number and the location of the binary critical points may correspond to different topological structure diagrams of isolines of the ternary mixture. Recommendations were made for testing topological structures of the diagrams of isolines of scalar properties of ternary mixtures built on the results of field measurements and precision calculations with the use of model equations.