What do the spacing of isoheights indicate?

The spacing of isoheights, which are lines on a weather map that connect points of equal height above sea level, primarily indicates the strength of the wind. When isoheights are closely spaced, it signifies that there is a steep vertical gradient, which typically correlates with stronger winds aloft. This is due to the changes in atmospheric pressure and density associated with altitude. A tight spacing of these lines suggests that the wind flows rapidly between the different heights, thereby indicating a stronger wind speed. Conversely, if the isoheights are widely spaced, it indicates a gentler slope and, thus, weaker winds.

The other options focus on aspects such as humidity, temperature, and atmospheric pressure, which can be analyzed on different types of maps or graphs but do not directly correlate with the spacing of isoheights. Instead, pressure systems are often illustrated with isobars on surface maps, while other factors like humidity and temperature are typically represented using different contour lines or patterns. The relationship between isoheight spacing and wind strength, however, is a fundamental aspect of analyzing upper-level atmospheric conditions.