How Many Decimal Places Are Needed for Latitude and Longitude to Achieve a 50-Foot Accuracy?

How Accurate Latitude and Longitude Storage Impacts Accuracy

In database design, the precision of latitude and longitude data storage directly translates to the accuracy of geographic locations. Decimal(9,6) is often recommended for this purpose, prompting the question of how accurate is necessary.

To determine the required accuracy, consider the tolerance range. For example, to achieve an accuracy within 50 feet, we need to know how many decimal places translate to that distance.

Relationship between Decimal Places and Accuracy

The World Geodetic System (WGS84) defines a unit of measure known as the "degree," which is approximately 111 kilometers (69 miles) at the equator. Each degree can be further divided into minutes and seconds, with each level of precision providing increased accuracy.

Decimal Place Conversion

Using the distance to degree relationship, we can calculate the approximate accuracy provided by each decimal place:

• 0 decimal places: 1,000 miles
• 1 decimal place: 100 miles
• 2 decimal places: 10 miles
• 3 decimal places: 1 mile
• 4 decimal places: 0.1 miles (5280 feet)
• 5 decimal places: 0.01 miles (528 feet)
• 6 decimal places: 0.001 miles (52.8 feet)
• 7 decimal places: 0.0001 miles (5.28 feet)
• 8 decimal places: 0.00001 miles (0.528 feet)

Optimal Accuracy for 50 Foot Tolerance

Based on the table above, to achieve an accuracy within 50 feet (5.28 feet), we would need to store latitude and longitude values with at least 6 decimal places.

The above is the detailed content of How Many Decimal Places Are Needed for Latitude and Longitude to Achieve a 50-Foot Accuracy?. For more information, please follow other related articles on the PHP Chinese website!