1. A method of estimating an impact of a software update, the method comprising: obtaining first usage measures for each executable line of source code of a first instance of a software application; analyzing the software update of the software application by comparing base source code for the software application to updated source code for the software application to determine differences between the base source code and the updated source code; identifying one or more executable source code lines of interest from the base source code based on the differences, the identified one or more executable source code lines of interest including: first executable lines of source code deleted from the base source code; second executable lines of source code in the base source code changed between the base source code and the updated source code; third executable lines of source code in the base source code located immediately before or after each executable line of source code added to the updated source code; and fourth executable lines of source code in the base source code that include a reference to a class or data structure containing one or more deleted, changed, or added lines of source code in the updated source code even when the fourth executable lines of source code are not changed; aggregating the first usage measures for each of the source code lines of interest by adding together counts included in the first usage measures for each source code line of interest; and estimating an impact of the software update based on the aggregated first usage measures; wherein the updated source code corresponds to source code for the software application after the software update is applied to the base source code.