The data that describes the heatmap value-to-color mapping is set in z. Data in z can either be a {2D array} of values (ragged or not) or a 1D array of values. In the case where z is a {2D array}, say that z has N rows and M columns. Then, by default, the resulting heatmap will have N partitions along the y axis and M partitions along the x axis. In other words, the i-th row/ j-th column cell in z is mapped to the i-th partition of the y axis (starting from the bottom of the plot) and the j-th partition of the x-axis (starting from the left of the plot). This behavior can be flipped by using transpose. Moreover, x (y) can be provided with M or M+1 (N or N+1) elements. If M (N), then the coordinates correspond to the center of the heatmap cells and the cells have equal width. If M+1 (N+1), then the coordinates correspond to the edges of the heatmap cells. In the case where z is a 1D {array}, the x and y coordinates must be provided in x and y respectively to form data triplets.