Phonetic and phonological databases
P-base is a database of several thousand sound patterns in 500+ languages. P-base database can be cited as Mielke, Jeff (2008) The Emergence of Distinctive Features. Oxford: Oxford University Press.
These are IPA charts in which area represents the crosslinguistic frequency of IPA symbols, according to the segment inventories in P-base. The figures were created using the Cart program, which is used to make density-equalizing maps like in The Atlas of the Real World. The density-equalization algorithm is described in Diffusion-based method for producing density equalizing maps, Michael T. Gastner and M. E. J. Newman, Proc. Natl. Acad. Sci. USA 101, 7499-7504 (2004).
We have been developing an objective measure of how similar various consonants and vowels are to each other. In this model, phonetic similarity is based on articulatory data from ultrasound, electroglottograph, and aerodynamic measurement, acoustic measures, and perceptual judgments (SSHRC grant #410-2007-0735, “Measuring the Phonetic Similarity of Speech Sounds”).
Here are some visualizations of the similarity data from an article in a Lingua special issue on phonological similarity.