Is a 1:250,000 base map scale appropriate for plotting field data to determine coal bed thickness and extent over a 50,000 acre site?

• A. No, because there is not adequate detail to accurately locate the coal beds
• B. Yes, it provides sufficient detail to locate the coal beds
• C. Yes, because coal beds are large-scale features
• D. No, because the scale is too large to show the coal beds

Answer: (A)

The key idea is map scale and the level of detail required for field measurements. A 1:250,000 base map is a small-scale map, meaning it shows broad, regional features rather than fine, local detail. When you’re trying to plot field data to determine coal bed thickness and lateral extent across a 50,000‑acre site, you need precise locations of bed boundaries and thickness measurements, which requires much higher detail than a 1:250,000 map can provide.

To see why, think about the distance represented by map measurements at that scale. One inch on the map covers about 3.95 miles on the ground, and one centimeter covers about 0.63 kilometers. That level of resolution is insufficient to locate narrow coal seams, their exact outcrop positions, and small thickness variations across the site. Determining thickness and extent reliably typically requires using larger-scale maps (for example 1:24,000 or finer) and integrating borehole data, outcrop mapping, and possibly geophysical information.

So this scale does not provide adequate detail for accurately locating coal beds and measuring their thickness across the area. The other options are not suitable because they either overstate the amount of detail provided by this scale, mischaracterize the scale as being too large, or rely on the assumption that large-scale features inherently yield sufficient detail, which isn’t the case for thickness and precise bed boundaries.