A Nonogram clue describes blocks of consecutive filled cells. You may also see those blocks called runs. Separate monochrome clue blocks need empty space between them, and confirmed empty cells can divide a line into smaller open segments.
These terms are simple, but keeping them precise prevents a lot of confusion in later techniques.
What is a block?
A block is one consecutive group of filled cells represented by one clue number.
For clue:
4
the line contains one four-cell block.
For clues:
2 3
the line contains two blocks:
- one 2-block;
- one 3-block.
The block lengths must match the clues exactly.
If four cells touch continuously, they form one 4-block, not two 2-blocks.
Is a run the same as a block?
In Nonogram discussions, run is commonly used as a technical synonym for a consecutive block of filled cells.
VeyraPlay prefers block in beginner-facing explanations because it connects naturally to clue numbers:
clue 5 represents a 5-cell block.
We may introduce run when discussing external terminology, algorithms, or formal descriptions, but the two words should not be alternated randomly as if they were different concepts.
What is a mandatory gap?
Two consecutive monochrome clue blocks must have at least one empty cell between them.
That required separation is the mandatory gap.
Clues:
3 2
therefore need at least:
■■■×■■
The two blocks contain 5 filled cells, but the complete minimum span is 6 because one separator is required.
If the line is longer, extra empty cells can appear before the first block, between blocks, or after the last block.
What is a separator?
A separator is a specific confirmed empty cell that keeps blocks distinct or closes a completed block.
The terms are related but useful in different ways:
- mandatory gap describes the spacing rule between clue blocks;
- separator describes an actual known empty boundary in the current puzzle state.
For example:
■■×■■■
The X is a separator between the 2-block and 3-block.
If a completed block sits away from another clue, an adjacent X can also serve as a boundary preventing the block from extending.
What is an open segment?
An open segment is a contiguous part of a line that has not been cut by confirmed empty cells and is still available to unresolved blocks.
Consider:
×????×???×
There are two open segments:
- cells 2–5, length 4;
- cells 7–9, length 3.
No block can cross any of the confirmed empty cells.
This vocabulary becomes especially useful when a line has several clues. You can ask which clue blocks can legally fit in which segments.
Why not call every open area a gap?
The word gap is used informally in many ways.
It might mean:
- required empty space between blocks;
- a stretch of unknown cells;
- an empty region between boundaries.
That ambiguity is harmless in casual play but awkward in precise teaching.
VeyraPlay therefore uses:
- mandatory gap for required spacing between clue blocks;
- separator for a confirmed empty boundary;
- open segment for a still-available contiguous region;
- gap only when the context is clear.
Blocks cannot merge
Suppose the clues are:
2 2
and you already know:
?■■?■■?
If the cell between the two filled pairs were filled, the line would contain one 5-cell run across the middle rather than two separate 2-blocks.
Once those pairs are correctly identified as the two clue blocks, the cell between them must be empty.
This is a basic example of merging prevention: preserving the required identity of separate clue blocks.
Blocks cannot extend beyond their clue
Suppose a single clue is 3 and you have established:
??■■■??
If those three filled cells are the clue block, neither adjacent cell can be filled.
Otherwise the block would become length 4.
The cells beside the completed block are forced empty.
This is why completed blocks and separators are closely linked.
Blocks have an order
For clues:
2 4 1
the clue blocks are not interchangeable.
There is:
- a first 2-block;
- a second 4-block;
- a final 1-block.
Their left-to-right or top-to-bottom order never changes.
Later techniques use this identity to determine that a particular filled cell can belong only to one clue, or that a particular segment must be reserved for a later block.
A block can be partly known
You may know that several filled cells belong to the same block without knowing the full block position.
For clue 5, a current state might include:
???■■????
Those two adjacent fills could be the middle, beginning, or end portion of the 5-block depending on other constraints.
The block is confirmed to pass through those cells, but it is not yet complete.
Techniques such as extending confirmed blocks and block reach reason from exactly this kind of partial information.
What is block reach?
The reach of a clue block is the set of cells that block can still legally occupy under the current constraints.
A cell outside the reach of every remaining block is forced empty.
A known filled cell that lies inside the reach of only one clue may help identify which block it belongs to.
You do not need to calculate reach formally as a beginner, but the idea explains many intermediate deductions.
Gaps can eliminate block placements
Suppose the largest remaining clue is 4.
An open segment of length 3 cannot contain that block.
If clue order and other segments show that no smaller remaining clue can use the segment either, the cells in that segment may become forced empty.
This is the basis of gap elimination.
The important comparison is always between:
- remaining clue lengths;
- segment lengths;
- clue order;
- known filled cells inside those segments.
Minimum span connects blocks and gaps
For clues 3 2 4:
- filled cells require
3 + 2 + 4 = 9; - mandatory separators require at least
2more cells; - minimum span is
11.
If the available segment has exactly 11 cells, every block and mandatory separator is fixed relative to that segment.
If the segment has 13 cells, there are 2 cells of slack that can be distributed around or between the blocks.
This relationship between block lengths, required gaps, and available space drives many line-solving techniques.
Common terminology mistakes
Calling any filled cluster a completed block
A cluster can be only part of a larger clue block. Completion requires the correct clue identity and exact length.
Treating run and block as different rules
They are usually synonyms for the same consecutive filled group.
Calling unknown space empty
An open segment contains cells still available to blocks. It is not an empty region.
Forgetting that the mandatory gap is a minimum
Blocks can be separated by more than one empty cell.
Ignoring clue order when assigning blocks
Size alone is not enough. Earlier and later clues must still fit in the correct sequence.
FAQ
What is a block in a Nonogram?
A block is a consecutive group of filled cells represented by one clue number.
What is a run in a Nonogram?
Run is a common technical synonym for a filled block.
How many empty cells must be between two blocks?
At least one in a standard monochrome Nonogram.
Can a gap contain more than one empty cell?
Yes. One cell is the minimum required separation.
What is an open segment?
A contiguous region of a line not cut by confirmed empty cells and still available to unresolved clue blocks.
Why do blocks need separators?
Without at least one empty cell between separate monochrome clue blocks, they would merge into one larger block.
What to learn next
The next natural techniques are Overlap, Edge Anchoring, Completed Blocks and Separators, and Gap Elimination.