A Mac address is a fixed number associated with a NICs onboard memory. It is initially assigned at the factory. The MAC address is broken up into 2 parts. The first part is the Block id which is six digit sequences that is unique to each vender. The second section is the device id which is created and assigned by the manufacture.

A Network layer address is different because there format based on the type of protocol and network used. Also, there unique id is based on a hierarchal addressing theme on subsets of data  and narrowing it down. Just like in an address you can narrow down your house, for example: Florida, Boca Raton, 33428, SW 53th street states that you live in Florida. You also live in the area located in Florida called Boca Raton and you are also in the area of 33428 which is located in Boca Raton. Finally you live on SW 8th street which is in the area of 33428 which is located in Boca Raton which is also located in Florida.