Thanks to the military’s Global Positioning System, border disputes — common in the nation’s frontier days — are making a comeback. The system, launched in the 1980s, is a cluster of 24 satellites, designed for targeting weapons and tracking troops. But in recent years it has revolutionized land surveys, making it easier and cheaper for even the smallest municipalities to pinpoint their boundaries.

Using GPS, projects that once required surveyors to lug compasses and heavy measuring chains across difficult terrain can now be finished in a few days. A single surveyor equipped with a $15,000 box that fits in a backpack is sometimes all it takes to define a once-murky border.

The new technology is raising thorny questions about boundary law — a largely uncharted hodgepodge of local, state and federal decisions based on land records, deeds, titles and treaties.