# GRIB学习笔记：样例文件分析 - Section 6

## Section 6: Bit-map Section

OctetsKeyTypeContent
1-4section6LengthunsignedLength of section in octets (nn)
5numberOfSectionunsignedNumber of section (6)
6bitMapIndicatorcodetableBit-map indicator (see Code Table 6.0 and Note 1)
7-nnBit-map - Contiguous bits with a bit to data point correspondence, ordered as defined in Section 3. A bit set equal to 1 implies the presence of a data value at the corresponding data point, whereas a value of 0 implies the absence of such a value.

## grib_dump示例

======================   SECTION_6 ( length=6, padding=0 )     ======================
1-4       section6Length = 6
5         numberOfSection = 6
6         bitMapIndicator = 255 [A bit map does not apply to this product (grib2/tables/4/6.0.table) ]


## 说明

1-4: section长度

5: section序号

6: bit-map标识符，由Code Table 6.0定义。