The meticulous hand-drawn and hand-colored maps were made by John Randel Jr., a surveyor, who had earlier mapped the Manhattan street grid and who superimposed those streets on the hills, valleys, watercourses and country homes that dotted the landscape north of Houston Street during the second decade of the 19th century.
Woodland-savannah vegetation is also found in the area but is ultimately restricted to shallow depressions and khors (seasonal watercourse)/valleys because of comparatively favourable ground water conditions.
Composed of limestones, the range is characterized by karstic features such as sinkholes, caves, dry valleys, and underground watercourses.
The hilly massif rarely exceeds 650 feet (200 m) in elevation but is slashed with numerous deep valleys formed by watercourses associated with the Aire and Aisne rivers, which constitute a barrier to transportation.
When he met with any valleys or deep watercourses crossing the line, he either caused them to be filled up with rubbish, or bridges to be built over them, so well levelled, that all being of an equal height on both sides, the work presented one uniform and beautiful prospect.
The watercourses are characterised by steep narrow valleys, which contributes to high rates of run-off, as does the underlying solid geology.
On the plateau the tree cover is broken by grass-covered dambos: shallow saucer-shaped valleys, often lacking a surface watercourse.
The region comprises a hilly area near the coast and an inland valley occupied by a seasonal watercourse, the Wadi Ḥaḍramawt, that runs parallel to the coast before turning southeastward to reach the sea.
The central part of the dam is perpendicular to the watercourse, while the extensions of the wall to either side curve back down the valleys approximately following the contour.
The paper's overseas edition said 264 villages lining watercourses in the hilly region of southern Shaanxi were completely washed away by floodwaters surging through the narrow valleys.
The valley's principal watercourses, the Nugaaleed and the more westerly Dheere, fill briefly during and after rainstorms (April to June) and drain into the Indian Ocean.
