This is a fundamental geographic fact about the dimensions of the Earth's graticule and requires no citation.
The claim states a basic mathematical and geodetic definition regarding the length of a degree of latitude or longitude at the Earth's equator ($1^\circ \approx 111\text{ km}$, so $0.001^\circ \approx 111\text{ m}$). This is trivially true by definition and everyday observation in cartography and geodesy, categorized as common knowledge. None of the retrieved papers specifically address or test this exact geodetic conversion factor as a hypothesis, making them tangential.