Figures are photographs, sketches, or drafted illustrations. They contain more than words and numbers. Tables are lists of words or numbers arranged in rows and columns. Figures have captions at the bottom and often have explanatory legends within their fields. Tables have titles at the top, and they may have notes at the bottom providing information necessary to understand the material.
Tables do note, however, have captions.
The caption of a figure should describe the figure. A rigorous caption would begin with words like Plot of C and O isotopic compositions of Pohick Valley carbonates . . . . Map of Sr concentration in groundwater of the East Lakedale Quadrangle . Slightly less rigorous but generally acceptable captions would begin with Variation in C and O isotopic compositions of Pohick Valley carbonates . . . . Sr concentration in groundwater of the East Lakedale Quadrangle . . .