NCEES PE Agricultural and Biological Engineering Remote Sensing, GIS & GNSS for Land & Water: practice questions

1 · GIS data models · medium

On the Mercator projection, the scale factor at latitude φ is sec φ. How much is area exaggerated at 60° latitude compared with the equator?

1. 1.4 times
2. 2 times
3. 8 times
4. 4 times

2 · Spatial analysis · medium

Computing the mean slope of each sub-watershed from a slope raster and a sub-watershed raster is an example of which map algebra operation?

1. A zonal operation
2. A local operation
3. A global operation
4. A focal operation

3 · Spatial analysis · hard

After intersecting a field-boundary layer with a soil-unit layer, many tiny thin polygons appear along boundaries that should coincide. What are they and how are they usually handled?

1. Sliver polygons; remove them with a cluster tolerance or by eliminating small polygons
2. Raster cells; convert them back to vector using a finer cell size
3. Buffer zones; keep them because they mark uncertainty along each boundary
4. Topology nodes; keep them because they record connectivity between arcs

4 · Digital elevation models and watershed delineation · hard

Why does automated D8 delineation often fail in flat, canal-irrigated plains, and what is a common remedy?

1. Flat plains have no sinks at all; the remedy is to skip the fill step in the processing sequence
2. Tiny height errors and artificial embankments dominate flow; burn in mapped drains and verify in the field
3. Canal plains have too many streams; the remedy is to raise the accumulation threshold tenfold
4. D8 cannot run on projected data; the remedy is to use geographic coordinates for the DEM

5 · GNSS · easy

A receiver's clock is in error by 1 microsecond. What range error does this produce?

1. About 300 m
2. About 0.3 m
3. About 30 km
4. About 3 m

6 · GNSS · medium

A farm needs centimetre-level positioning for auto-steer tractors and laying subsurface drain lines. Which technique is appropriate?

1. Autonomous single-frequency code positioning with a handheld receiver
2. Code-based differential GNSS from a radio beacon about 200 km away
3. RTK using carrier-phase corrections from a base or reference network
4. Wide-area SBAS corrections from a geostationary satellite broadcast

7 · GNSS · hard

A surveyor notices that PDOP rises sharply when most visible satellites are clustered low in the eastern sky. Why?

1. Clustered satellites broadcast on the same frequency and jam each other's signals
2. Clustered satellites give poor geometry, so range errors map into large position errors
3. Low satellites are closer to the receiver, which shortens the ranges below the error level
4. Low satellites always have more accurate clocks, which disturbs the least-squares solution

8 · Applications to watershed, irrigation and erosion mapping · easy

A basin has 24 first-order and 6 second-order streams. What is the bifurcation ratio between these orders?

1. 18
2. 4.0
3. 0.25
4. 3.0

9 · GIS data models · medium

What is a triangulated irregular network (TIN)?

1. A network of stream lines coded by Strahler order for hydrological analysis
2. A raster of equal square cells, each storing a single height value for its area
3. A surface model of non-overlapping triangles joining irregularly spaced height points
4. A set of contour lines stored as closed polygons with a height attribute each

10 · Spatial analysis · medium

Reclassifying a slope raster into classes 1 (0–3%), 2 (3–8%) and 3 (above 8%) is an example of

1. a local operation that changes each cell's value independently of its neighbours
2. a global operation that needs every cell to compute the value of each cell
3. a focal operation that uses a moving 3 × 3 window around each cell
4. a zonal operation that summarises values inside separate polygon zones