What's is the meaning of the *alignment* inside the partition_table.h?

Take the 4M\partition_table.h for example.

 #define NVMS_FIRMWARE_PART_START 0x002000 /* Alignment to 512KB is dictated by the default FLASH_REGION_SIZE. */ #define NVMS_FIRMWARE_PART_SIZE 0x07E000 /* +----------------512KB---------------------+ */ #define NVMS_GENERIC_PART_START 0x0E0000 #define NVMS_GENERIC_PART_SIZE 0x020000

The firmware part is start at 0x2000 which is not aligned to 512KB, the generic part is not, too. And why the generic part suddenly jump to 0xE0000 while the end address of the firmware part is 0x80000?

Another question is, Can I arrange a smaller firmware part, which is about 128KB, for my secondary bootloader, and arrange a bigger partition part, which is about 2MB, for my application at the same time? How should I modify the partition_table.h?

Thanks!