The percentage of rural population by residence has always been very high, with significant differences between geographic regions, ranging in the 1980s from a high of about 70 percent in the central region to a low of 40 percent in Southern Croatia. Traditionally, there were wide differences among different settlements in the house style and interior design. Today, however, there is a tendency toward uniformity. Settlements are either clustered (mainly in the north and south) or dispersed (mainly in the hinterland of the south and Central regions). Clustered settlements are either compact and centered on a square or stripped into perpendicular streets. In the south, houses are made of stone, with roofs of reed (the oldest tradition), stone slabs, or convex tiles (the newest tradition). They are usually two-story buildings along the coast and one-story buildings in the coastal hinterland. Elsewhere, the material is wood (oak logs or trimmed wooden planks), clay mixed with chaff, or more recently brick (at first adobe) and concrete. The roofs are covered either with shingles, thatch, or flat tiles (the most recent tradition). Houses were one-story buildings.