the level sea of什么意思

Soapy left his beach and strolled out of the square and across the level sea of asphalt.

Soapy left his bench and strolled out of the square and across the level sea of asphalt, where Broadway and Fifth Avenue flow together.
索比离开长凳，踱出广场，跨过百老汇大街和第五大街的交汇处那片沥青铺就的平坦路面。