In recent years a mix of Open Data and commercial sources have been used to build geodemographic classifications of neighbourhoods. In this paper we argue that geodemographics are coming to embody new thinking about the emergent mixed Big Data economy. This has implications for openness and full scientific reproducibility of classifications, as well as the engagement of stakeholders in the process of building classifications. We propose and implement an operational framework for blending open and other data sources that can stimulate development of classifications that are more timely and data rich yet sufficiently open to peer scrutiny. We illustrate these ideas and challenges by describing the creation and content of the London Workplace Zone Classification.