What is the difference between ospf single area and ospf multi-area?

In OSPF, intra-area links take precedence over inter-area links during route selection even when the inter-area links are shorter than the intra-area links. Each OSPF interface belongs to only one area. As a result, even when a high-speed link exists in an area, traffic of another area cannot be forwarded along the link. A common method used to solve this problem is to configure multiple sub-interfaces and add them to different areas. However, this method has a defect that an independent IP address needs to be configured for each sub-interface and then is advertised, which increases the total number of routes. In this situation, OSPF multi-area adjacency is introduced.