RPLS Technical Standards and Specifications 3 — Questions and Answers
Question 1: The National Map Accuracy Standards (NMAS) specify that for maps at scales larger than 1:20,000, no more than 10% of tested points may be in error by more than:
- 1/30 inch at publication scale (Correct answer)
- 1/50 inch at publication scale
- 1/100 inch at publication scale
- 1/10 inch at publication scale
Correct answer: 1/30 inch at publication scale
NMAS horizontal accuracy for maps larger than 1:20,000 requires that 90% of tested points fall within 1/30 inch of their true position at publication scale.
Question 2: What is the primary purpose of a 'datum' in surveying?
- A reference surface from which elevations or positions are measured (Correct answer)
- The instrument height above the ground
- A type of horizontal control monument
- The angular difference between true and magnetic north
Correct answer: A reference surface from which elevations or positions are measured
A datum is a defined reference surface (horizontal or vertical) from which all measurements in a survey are referenced.
Question 3: According to NGS specifications, what is the difference between a benchmark and a bench mark?
- They are the same; 'benchmark' is the common spelling and 'bench mark' is the NGS official spelling (Correct answer)
- A benchmark is a vertical control point; a bench mark is a horizontal control point
- A benchmark is temporary; a bench mark is permanent
- A benchmark has a known elevation; a bench mark has a known coordinate
Correct answer: They are the same; 'benchmark' is the common spelling and 'bench mark' is the NGS official spelling
NGS officially uses 'bench mark' (two words) for vertical control monuments, though 'benchmark' (one word) is widely accepted as equivalent.
Question 4: In a stadia survey, if the stadia interval factor is 100 and the rod interval is 1.52 feet, what is the horizontal distance to a level rod?
- 152 feet (Correct answer)
- 100 feet
- 15.2 feet
- 1520 feet
Correct answer: 152 feet
Horizontal stadia distance = rod interval × stadia constant = 1.52 × 100 = 152 feet when the line of sight is horizontal.
Question 5: Which specification governs the accuracy and content of FEMA Flood Insurance Rate Maps (FIRMs)?
- FEMA Guidelines and Specifications for Flood Hazard Mapping Partners (Correct answer)
- ALTA/NSPS Minimum Standards
- ASPRS Accuracy Standards
- NGS Geodetic Control Survey Standards
Correct answer: FEMA Guidelines and Specifications for Flood Hazard Mapping Partners
FEMA's Guidelines and Specifications for Flood Hazard Mapping Partners define the technical requirements for FIRM production and maintenance.
Question 6: A traverse with a linear closure of 1:10,000 means:
- The error of closure is 1 unit for every 10,000 units traversed (Correct answer)
- The traverse closes within 10,000 feet
- The angular error is 1 second per 10,000 feet
- The allowable misclosure is 0.001 feet per station
Correct answer: The error of closure is 1 unit for every 10,000 units traversed
A precision ratio of 1:10,000 indicates that the linear error of closure is 1 unit for every 10,000 units of total traverse length.
Question 7: Under ASPRS Accuracy Standards for Digital Geospatial Data (2014), the Vertical Accuracy Class is defined using which statistical measure?
- RMSEz (Root Mean Square Error of vertical component) (Correct answer)
- Standard deviation of the mean
- Maximum absolute error
- 95th percentile error
Correct answer: RMSEz (Root Mean Square Error of vertical component)
ASPRS 2014 standards define vertical accuracy classes based on RMSEz, the root mean square error of the vertical component.
RPLS Technical Standards and Specifications 3
The National Map Accuracy Standards (NMAS) specify that for maps at scales larger than 1:20,000, no more than 10% of tested points may be in error by more than: