Fig. 2.

Description information based on variable data mapping. The lowest Y is in Humbang Hasundutan Regency, and the highest Y is in Batubara Regency. The lowest ${\mathrm{X}}_1$is in Deli Serdang Regency, and the highest ${\mathrm{X}}_1$ is in West Nias Regency. The lowest ${\mathrm{X}}_2$ is in South Nias Regency, and the highest ${\mathrm{X}}_2$ is in Binjai City. The lowest ${\mathrm{X}}_3$ is in Pakpak Bharat Regency, and the highest ${\mathrm{X}}_3$ is in Medan City. The lowest ${\mathrm{X}}_4$ is in Humbang Hasundutan Regency, and the highest ${\mathrm{X}}_4$ is in Gunungsitoli City. The lowest ${\mathrm{X}}_5$is in West Nias Regency, and the highest ${\mathrm{X}}_5$ is in Medan City. The lowest ${\mathrm{X}}_6$ is in Padang Sidimpuan Regency, and the highest ${\mathrm{X}}_6$ is Pematangsiantar City. And the lowest ${\mathrm{X}}_7$ is Nias, and the highest ${\mathrm{X}}_7$ is in Medan City.