The sysusages table in the master database keeps track of the space you assign to all SAP ASE databases.
create database and alter database allocate new space to the database by adding a row to sysusages for each database device or device fragment. When you allocate only a portion of the space on a device with create or alter database, that portion is called a fragment.
sp_addsegment, sp_dropsegment, and sp_extendsegment change the segmap column in sysusages for the device that is mapped or unmapped to a segment. See System Administration Guide: Volume 2 > Creating and Using Segments.