What Does It Mean for a State to Border Another State?

Two states border each other when their territorial boundaries share a common edge or line of contact.

Types of Borders

• Land borders: Contiguous territory meeting at a line (most common)
• Water borders: Shared lakes, rivers, or maritime boundaries
• Mixed: Combination (e.g., US-Canada: land + Great Lakes + maritime)

Border Characteristics

• Defined by: Treaties, surveys, natural features (watersheds, thalweg), coordinates
• Marked by: Monuments, buoys, fences, walls, or nothing (open)
• Governed by: International law (states) or constitutional law (subnational)

Implications of Bordering

• Legal: Jurisdiction, extradition, cross-border crimes, tax treaties
• Economic: Trade, labor markets, currency exchange, supply chains
• Social: Migration, families, culture, language, cross-border cooperation
• Environmental: Shared watersheds, airsheds, ecosystems, pollution
• Security: Defense, smuggling, trafficking, pandemic response

Subnational vs. International

Notable Examples

• Four Corners: Only US quadripoint (AZ, CO, NM, UT)
• Longest international: US-Canada (8,891 km)
• Shortest international: Botswana-Zambia (150 m)
• Most borders: China, Russia (14 each)