This paper reports in closed form the similarity heatfunctions \(H\) for laminar boundary layer flow on a flat wall. Plots of the constant-\(H\) lines (`heatlines') show that the path of convection from a hot free stream to a cold wall is unlike the path of convection from a hot wall to a cold fluid. As a supplementary contribution, the paper reports the exact similarity solution for the wall with uniform flux as the Prandtl number \(Pr\) tends to 0, and proposes a closed-form local Nusselt number correlation that covers the entire \(Pr\) range.