Captions should appear in sentence case. They should not end with punctuation unless the caption is a complete sentence.
Captions are bold and numbered, with a period and a space following the number. If you use the styles correctly, this will happen automatically.
Figure 1. Water use per barrel of oil
Numbering is consecutive throughout the document, including the appendices. (Meaning, if the last table in the main body is numbered 5, then the first table in the appendices would be numbered 6.) Avoid by-section numbering and other complex schemes unless the document is particularly long and complex itself.
Figure captions appear below the figure. Table captions appear above the table.
Any annotations or labels on the diagrams themselves should be sentence case and as brief as possible. Put any necessary explanations in the caption.
Avoid multipart figures if you can. When used, be sure each part is clearly labelled (usually with lowercase letters) and that each part is referenced and described in the caption.
For long captions, ensure that the first sentence or phrase completely describes the figure or table. The bolded text below is what would be put in the table of contents.
Figure 7. Landsat TM 4 imagery coverage for Alberta; scenes are outlined in green; scenes filled in with yellow are available from the Resource Data Division of the Alberta Department of Sustainable Development.
Because figures and tables can be extracted for use in presentations and other documents, make the captions as self-standing as possible. That means considering things like the following:
Avoid acronyms that are not widely know. Spell the terms out.
Location information should include Alberta preceded by an adjective that specifies the part of the province (e.g., south-central, southeastern).
If the figure or table has been repurposed from another document, even if it has been modified, then that should be stated at the end of the caption in parentheses.
Figure 1. Local study area (from Company 2010, figure 5)
Table 1. Equipment inventory with associated weighted values (modified from Company 2010, table 3)