Joanna Drucker’s “Humanities Approaches to Graphical Display,” a classic among critical digital humanists, is ostensibly a paper on visualization, with nice, original figures. The author discusses the implicits of “objective” visualizations; those often endorse simple conceptions of time (e.g. linear or even with no past) and categories (exclusive from one another, with firm boundaries, etc.). Doing this, she in fact addresses the implicits of “objective” categorization generally – and she explicity makes the point that data are capta (constructed), that humanists know this and that using computers/quantification should not make them forget it. Her paper might free your imagination for the categorization of your own data.
Marten Düring’s “From Hermeneutics to Data to Networks” is based on the same idea of not applying supposedly objective categories, but devising a coding scheme based on specific data and research questions. It very clearly guides you through the non-straightforward process (which occupied a large part of his PhD research) of categorizing help provided to Jews in Nazi Germany. The section on categorization is relevant for all research in historical sources and probably all research in the humanities and social sciences – even if you do not care about networks.