Hourly Area Prediction (HAP) charts are designed for communications between a specified base station location, and another station located within a nominated area. The HAP chart is a guide to frequency selection for HF communications between a specified station and a base station, in this case Seattle. The recommended frequency for communications with the base at a given hour is read off from the point in the map corresponding to the mobile's location. The predictions are made from real time data which are updated each hour. If present, dashed lines delineate areas of unlikely communication.