Western Europe is the best documented region in this atlas, and the reason is a technology. Printing arrived in the middle of the fifteenth century and the religious upheaval of the following century was conducted through it: theses, catechisms, confessions, vernacular bibles, polemics answered within weeks, and cheap woodcut pamphlets aimed at readers who could not read Latin.
The consequence for the record is abundance of a particular kind. Doctrinal positions are stated with unusual precision because they were being defended in public against opponents who would quote them back. Institutional history is traceable in detail because both sides kept archives. Parish registers, visitation records and consistory minutes let a historian follow religion down to the level of a village and a year, which is possible almost nowhere else before the modern period.
What that abundance obscures is what nobody wrote down. Practice that was neither approved nor prosecuted leaves little trace, and the unofficial religion of charms, cunning folk and local shrines appears mainly when an authority objected to it. The witch trials produced enormously detailed records for exactly this reason, and they describe a set of beliefs shaped by the questions asked as much as by anything the accused held.
The region also exported its categories. The vocabulary this atlas uses, religion, doctrine, superstition, was formed in these arguments, and applying it elsewhere carries assumptions made here.