The correct answer is C) Compressor map. Compressor characteristics are normally summarized in the form of a compressor map, which is a graphical representation of the compressor's performance. This map typically shows the relationship between the compressor's pressure ratio, mass flow rate, rotational speed, and efficiency. The compressor map allows engineers to understand the compressor's operating range, surge and choke limits, and overall performance, which is crucial for the design and optimization of various systems that use compressors. The other options are incorrect because a Venn diagram is not used to represent compressor characteristics (A), a straight line graph would not adequately capture the complex relationships between compressor parameters (B), and a spreadsheet is simply a data storage and calculation tool, not a graphical representation of compressor performance (D).