Read this.

Public libraries are essential to communities. And yet public libraries are always woefully underfunded, and the first program to suffer municipal budget cuts.

Everyone knows, in theory, that libraries are important to the very communities who limit or cut their funding. It may be because it is so difficult to empirically or quantifiably measure the impact a library system has on a city or community.

The Friends of the San Francisco Public Library thought about that, and engaged a Seattle firm to investigate and quantify some of the benefits of the SFPL system. Without including the immeasurable and intangible benefits of the libraries on their communities, the firm found that from what it could quantify, the San Francisco Public Library returns to the City an astounding $3.34 on the dollar for the money invested.

From the press release:

A study released today by the Friends of the San Francisco Public Library describes the diverse contributions and quantifies the substantial value that the San Francisco Public Library provides to San Francisco. Through an examination of an array of library benefits, the study reveals that the SFPL generates an impressive return of $3.34 for every dollar spent on its operations and services.