Space needed for a title may vary from one year to the next. The Census Bureau shelves are a case in point. Every ten years the Census of Population and Housing demands a great deal of space, while every five years the Census of Economics and the Census of Agriculture quickly fill more space. To add to the confusion, parts of series are housed in different locations within the broader collection as a consequence of changes in issuing agencies and SuDocs classification. Changes in format also alter space requirements.
New technologies store significantly more data in substantially less space than earlier.
Consequentially, formulas used to calculate collection growth cannot be easily applied to predict adequate shelf space. The document library community was shocked when in 1995 GPO released its plans to migrate to electronic formats. Librarians questioned their conventional thoughts on space planning. In thinking about future space, it is important to consider current requirements. Shelving items is not easy as workers insert slick pamphlets next to stapled monographs and folded maps next to odd sized kits.