Much of the sociolinguistic and stylistic variation which is of interest to linguists is phonetic in nature, but the access route to corpus data is typically via a textual transcription. This poses a significant problem for a researcher who wishes to access the original recordings of speech in order to analyse variation: how can they search for relevant data? Many transcription traditions allow for the representation of such variation through non-standard orthography, and such conventions should therefore allow access to data relevant to the study of variation. However, the specific conventions used vary between traditions (and indeed may not be applied consistently by individual transcribers). This then creates another problem where the researcher wishes to access data across an aggregated collection, which is a practical necessity given the relatively limited size of most corpora of spoken language. In this paper, we analyse the conventions used in two of the component collections in the Australian National Corpus, the Australian Radio Talkback Corpus and the Monash Corpus of Spoken English. On the basis of this analysis, we develop a fragment of an ontology which gives an explicit account of the phenomena related to non-standard pronunciation represented in the transcripts and which can therefore act as the basis for better searching of the collections and better access to relevant data for analysing sociolinguistic and stylistic variation.