Pump Flow calculation

afa13

Hello,
When selecting a pump one should calculate the flow rate of the building supplied. To determine the building's supply one should select the longest piping distance and the the area where the most flow is required, right?
or it can be multiple areas «, or one should select all the areas supplied by the pipeline....the latter would require an enormous amount of flow whereas selecting the are with the most flow and that with the most head will result in a more economic decision, right?