The ornamental design for a heatingplate, as shown and described.
FIG. 1 is a perspective view of a heating plate showing my new design;
FIG. 2 is a second perspective view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a front view thereof, the back, left side, and right side views being identical thereto; and,
FIG. 5 is a side view thereof rotated about its central vertical axis approximately 45 degrees from the position shown in FIG. 4.
The appearance of the bottom side forms no part of the claimed design. The broken lines in FIGS. 2, 4, and 5 represent unclaimed boundaries of the design. The broken lines in FIG. 1 are for environmental purposes only and form no part of the claimed design.