Pematangsiantar, and also known as the City of Pematangsiantar, is an independent city in North Sumatra Province of Indonesia, surrounded by, but not part of, the Simalungun Regency, making Pematangsiantar an enclave within Simalungun Regency. Pematangsiantar formerly had the status of a second-level district and was the administrative centre of the surrounding Regency, but in 1986 it was elevated to Kota (City) and separated from the Regency.

North Sumatra is a province of Indonesia located in the northern part of the island of Sumatra. Its capital and largest city is Medan. It is bordered by Aceh on the northwest and Riau and West Sumatra on the southeast, with two different coastlines located on the Indian Ocean and the Strait of Malacca, and a maritime border with Malaysia to the east. North Sumatra is Indonesia's fourth most populous province after West Java, East Java, and Central Java, and is also the most populous province outside of Java Island. North Sumatra is also the third-largest province in area on the island of Sumatra after South Sumatra and Riau provinces. It covers an area of 72,460.74 km2, which is approximately the same size as Sierra Leone or Scotland or Maine.