Data compaction and data expansion methods for an electron beam direct writing system EBM-130V are described. EBM-130V adopts the raster scan method using a variably shaped line beam. The system does not have an effective hierarchical structure in its data format, because it has only a single deflector. So, an extra virtual layer has been introduced into the EB data format, and an artificial hierarchical data structure is used for data compaction. The compacted data is expanded by an EB control software system. For a 4 Mbit DRAM, the data amount was about 30 MBytes (compaction rate 1/16), the data conversion time was about 12 minutes (reduction rate 1/35), and the data transfer time from the system disk to the pattern data memory was reduced to about 1/5, by using the date compaction method.