I noticed that the heatmap was not properly plotted for a  dataset. Steps:

1. search WISE multiepoch photometry table with ploygon (0 -1, 0 1, 1 1, 1 -1), returned  1,376,008 sources.
2. the heatmap X-axis ranges from (360, 0) which caused the heatmap displayed at the way right hand side
3. when I specify the ratio to be 1 (or 2), nothing seems to be displayed. 
4. if I do any filter on it by draw a rectangle, the resulting plot is very faint and barely visible.
5. when I applied [Xmin, xmax]to [0, 1], there was nothing plotted, although there was 173,368 rows in the table