# 11.11.1 Pillars and Columns

Topic Version | 1 | Published | 09/11/2015 | |

For Standard | RESQML v2.0.1 |

Pillars and columns describe the 2D topology of the grid.

- For IJK grids, each column has four pillars,
- For unstructured column-layer grids, each column is defined by a list of three or more pillars for each column.
- For an unfaulted grid, each pillar has one corresponding coordinate line.
- For faulted grids each pillar requires additional “split” coordinate lines.
- For a faulted IJK grid each pillar can have up to four coordinate lines per pillar.
- For faulted unstructured column-layer grids, each pillar may have as many coordinate lines as there are adjacent columns.

- The number of nodes per coordinate line is fixed at NKL = NK + GapCount + 1, and provides the topological support for the node geometry of the grid with an array of CoordinateLineCount x NKL points.