US Survey Feet (ft-us) to Nautical Miles (nMi) conversion

What is us survey feet?

What is US Survey Feet?

US Survey Feet is a unit of length used in the United States for land surveying. It is slightly different from the international foot. Understanding its origin and applications is crucial for accurate land measurements and legal descriptions.

Origin and Definition

The US Survey Foot (ftUS) is defined based on the Mendenhall Order of 1893, which related customary units to the metric system using the meter. At that time, it was defined as:

1 US Survey Foot = $\frac{3937}{1200}$ meters

This value equates to approximately 0.3048006096 meters. This differs slightly from the international foot which is exactly 0.3048 meters. The difference, while seemingly small (2 parts per million), can accumulate significantly over large distances, impacting land boundaries and area calculations.

The Issue & Readjustment

The difference between the international foot and the US survey foot caused discrepancies, especially in states that relied heavily on the Public Land Survey System (PLSS). Over time, states have addressed this issue in various ways:

• Many states have officially adopted the international foot for all new surveys.
• Some states continue to use the US Survey Foot. It's crucial to know which definition is in use for any particular survey or land description.
• Conversion factors are often provided in legal documents to clarify which foot is being used.

For more information about each state's definitions of feet, please read NOAA's definition of US Survey foot.

Usage and Real-World Examples

While its use is declining, the US Survey Foot is still relevant in some contexts, especially when dealing with older surveys and legal descriptions. Understanding its magnitude helps grasp spatial relationships:

• Property Boundaries: In states where it is still used, a land description stating a lot is 100 US Survey Feet wide means it is approximately 30.48006096 meters wide.
• Land Area Calculations: Area calculations, like acres, derived from measurements in US Survey Feet will differ slightly from those derived from international feet.
• Geographic Information Systems (GIS): GIS databases may contain data referenced to US Survey Feet, requiring proper transformation when integrating with data using the international foot.

Interesting Facts

• The slight difference between the two definitions of a foot has caused legal disputes related to property boundaries.
• The National Geodetic Survey (NGS) provides tools and resources for converting between the US Survey Foot and the international foot.

What is nautical miles?

Here's a breakdown of nautical miles, designed for clarity, SEO, and user understanding.

Understanding Nautical Miles

Nautical miles are a unit of length used primarily in navigation, particularly in maritime and aviation contexts. It is based on the Earth's circumference and is closely related to the degree measurements of latitude and longitude.

Definition and Formation

A nautical mile is defined as the arc length on the Earth's surface that corresponds to one minute of latitude. Since one degree of latitude is approximately 60 nautical miles, one nautical mile is approximately 1/60th of a degree of latitude.

• Length: One nautical mile is approximately 1,852 meters (about 1.15 statute miles or 6,076 feet).
• Origin: The nautical mile's connection to latitude makes it incredibly useful for navigation because it directly relates to the Earth's spherical coordinates.

Why Use Nautical Miles?

The primary advantage of using nautical miles is its simplicity in navigation calculations. Because it is based on the Earth's degrees of latitude, distances on nautical charts can be easily measured using dividers and the latitude scale.

Formula

While there isn't a direct formula to "calculate" a nautical mile (it's a defined unit), you can convert between nautical miles and other units using the following approximate conversions:

• 1 Nautical Mile ≈ 1.15 Statute Miles
• 1 Nautical Mile = 1852 meters = 1.852 kilometers
• 1 Statute Mile ≈ 0.87 Nautical Miles

Notable Associations and History

• Early Navigation: The concept of the nautical mile has been used for centuries, predating the standardization of metric units. It provided a practical way for sailors to measure distances at sea.
• International Hydrographic Organization (IHO): The IHO officially defined the nautical mile as exactly 1,852 meters in 1929.

Real-World Examples and Applications

• Maritime Navigation: Used extensively for plotting courses, determining distances to ports, and calculating speed at sea (knots, where 1 knot = 1 nautical mile per hour).
• Aviation: Pilots use nautical miles for flight planning, calculating distances between airports, and determining airspeed and ground speed.
• Territorial Waters: Many countries define their territorial waters and exclusive economic zones (EEZ) in terms of nautical miles from their coastlines. A common limit is 12 nautical miles for territorial waters and 200 nautical miles for EEZ.

Examples

• Distance between cities: The distance between New York and London is about 3,000 nautical miles.
• Shipping routes: Major shipping routes are measured in nautical miles to plan transit times and fuel consumption.
• Fishing zones: Governments use nautical miles to define fishing zones and manage marine resources.