context: Along the Mediterranean coast is a strip of land, well-enough watered to support grazing for camels and sheep; digging for water generally succeeds but wells and cisterns are often far apart and sometimes unexpectedly dry. The earth is dusty in summer and glutinous in the rainy season from December to March, when the days are relatively cool and night bitter cold. South of the coastal strip is a bare limestone plateau, about 50 mi  wide at Dabaa and 150 mi  broad at Sollum. To the south lies the desert, with sand dunes for several hundred miles. Siwa Oasis, a Senussi stronghold, lies 160 mi  south of Sollum on the edge of the sand sea and to the east are a string of oases, some close enough to the Nile Valley to be in range of Senussi raiders mounted on camels. A standard-gauge railway ran along the coast from Alexandria, intended to terminate at Sollum, which in 1915 had reached Dabaa, from which ran a track, known as the Khedival Motor Road, which was motorable in dry weather, although when hostilities began the wet season was imminent. The western frontier of Egypt had not been defined in 1914 because negotiations with the Ottomans had been interrupted by the Italo-Turkish War  and then negated by the cession of Tripoli to Italy. A notional frontier ran south from Sollum, to the east of which was an area of 200,000 sq mi  all desert south of the semi-desert coastal strip but with several oases, some quite big and supporting sizeable populations, administered by the Egyptian government. Bedouin lived a nomadic life between the oases, traded with the inhabitants and took refuge at them when wells ran dry.
question: Which direction is the coastal limestone plateau the longest in miles,  50 miles wide or 150 milesbroad?
answer: broad