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We chose to work, at least to start, only with data in which every occurrence record is based on the existence of a preserved specimen in a museum. If there are ever any questions about the identification of the specimens, we can simply examine them and verify the data. Museums also typically record detailed spatial and temporal data for every specimen collection, while most every other data source summarizes these data in one way or another.
Over 40 Many museums contributed their data, however, since data quality, basic data definitions, and formats vary greatly among donor institutions we dedicated large amounts of time to basic data compilation and management, and standardization of data formats and definitions among all contributing institutions. Basic steps in our data manipulation are briefly described in the pages in this section (often with links to more detail).