Bearing in mind that I\'ll be performing calculations on lat / long pairs, what datatype is best suited for use with a MySQL database?
Use DECIMAL(8,6) for latitude (90 to -90 degrees) and DECIMAL(9,6) for longitude (180 to -180 degrees). 6 decimal places is fine for most applications. Both should be "signed" to allow for negative values.
DECIMAL(8,6)
DECIMAL(9,6)