The area under the graph can be calculated by: using geometry (if the lines of the graph are straight) counting the squares beneath the line (particularly if the lines of the graph are curved) ...

\(gradient = \frac{change~in~y}{change~in~x} = \frac{change~in~distance}{change~in~time} = \frac{change~in~metres}{change~in~seconds} = m/s.\) The gradient of a distance-time graph represents speed.