Currently, two-thirds of the Algerian population lives in the northern part of the country representing 4% of the entire territory. To provide needs of this population, the extension of the urban area of coastal has constantly expanding. As the capital and central core of the economy, Algiers is home to around 3 million people. To structure the inevitable expansion of Algiers, the government has put in place urban and coastal planning policies and enacted a set of laws regulating these urban planning. In order to illustrate the importance of urban expansion to the detriment of natural areas, a diachronic study is applied on the bay of Algiers. Geographic Information System (GIS) and imagery are used to assess the expansion of the mineral element and the necessity opening the bay of Algiers and its infrastructures onto the sea. It aims to quantify and illustrate the diversion of coastal land towards buildings. The study shows a constant expansion of the mineral element to the detriment of the plant element. Analysis of a few examples of projects shows that they do not always meet the need for a Mediterranean city and sustainability concepts.