The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.
Please refer to the change log for a documentation of changes to this specification.
PMTiles is a single-file archive format for tiled data. It enables low-cost, zero-maintenance map applications for "serverless" environments without having to rely on a custom tile backend or a third-party provider. This is achieved by packing all tiles of a tileset into an archive so that all tiles can be accessed easily and without much overhead via HTTP range requests. By combining all the tiles into one archive, hosting costs are kept low, as it is usually a lot cheaper to update one large file than to update thousands or even millions of small files.
An archive consists of five main sections:
- A fixed-size 127-byte header (described in Chapter 3)
- A root directory (described in Chapter 4)
- JSON metadata (described in Chapter 5)
- Optional leaf directories (described in Chapter 4)
- The actual tile data
These sections are normally in the same order as in the list above, but theoretically, it is possible to relocate all sections other than the header arbitrarily. The only two restrictions are that the header is at the start of the archive and the root directory MUST be contained in the first 16,384 bytes (16 KB) of the archive so that latency-optimized clients can retrieve the root directory in advance and ensure that it is complete.
Root Directory Meta Data Leaf Directories Tile Data
Length Length Length Length
<--------------> <---------> <----------------> <--------->
+--------+----------------+-----------+------------------+-----------+
| | | | | |
| Header | Root Directory | Meta Data | Leaf Directories | Tile Data |
| | | | | |
+--------+----------------+-----------+------------------+-----------+
^ ^ ^ ^
Root Dir Meta Data Leaf Dirs Tile Data
Offset Offset Offset Offset
The Header has a length of 127 bytes and is always at the start of the archive. It includes the most important metadata and everything needed to decode the rest of the PMTiles archive properly.
Offset 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000000 | Magic Number | V | Root Directory Offset |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000010 | Root Directory Length | Metadata Offset |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000020 | Metadata Length | Leaf Directories Offset |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000030 | Leaf Directories Length | Tile Data Offset |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000040 | Tile Data Length | Num of Addressed Tiles |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000050 | Number of Tile Entries | Number of Tile Contents |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000060 | C | IC | TC | TT |MinZ|MaxZ| Min Position | Max
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
000070 Position |CenZ| Center Position |
+----+----+----+----+----+----+----+----+----+----+----+----+----+----+----+
The magic number is a fixed 7-byte field whose value is always PMTiles in UTF-8 encoding (0x50 0x4D 0x54 0x69 0x6C 0x65 0x73)
The version is a fixed 1-byte field whose value is always 3 (0x03).
The Root Directory Offset is an 8-byte field whose value gives the offset of the first byte of the root directory. This address offset is relative to the first byte of the archive.
This field is encoded as a little-endian 64-bit unsigned integer.
The Root Directory Length is an 8-byte field specifying the number of bytes in the root directory.
This field is encoded as a little-endian 64-bit unsigned integer.
The Metadata Offset is an 8-byte field whose value gives the offset of the first byte of the metadata. This address offset is relative to the first byte of the archive.
This field is encoded as a little-endian 64-bit unsigned integer.
The Metadata Length is an 8-byte field specifying the number of bytes of the metadata.
This field is encoded as a little-endian 64-bit unsigned integer.
The Leaf Directories Offset is an 8-byte field whose value gives the offset of the first byte of the leaf directories. This address offset is relative to the first byte of the archive.
This field is encoded as a little-endian 64-bit unsigned integer.
The Leaf Directories Length is an 8-byte field specifying the accumulated size (in bytes) of all leaf directories. A value of 0 indicates that there are no leaf directories included in this PMTiles archive.
This field is encoded as a little-endian 64-bit unsigned integer.
The Tile Data Offset is an 8-byte field whose value gives the offset of the first byte of the tile data. This address offset is relative to the first byte of the archive.
This field is encoded as a little-endian 64-bit unsigned integer.
The Tile Data Length is an 8-byte field specifying the accumulated size (in bytes) of all tiles in the tile data section.
This field is encoded as a little-endian 64-bit unsigned integer.
The Number of Addressed Tiles is an 8-byte field specifying the total number of tiles that are addressable in the PMTiles archive (before Run-Length encoding).
A value of 0 indicates that the number is unknown.
This field is encoded as a little-endian 64-bit unsigned integer.
The Number of Tile Entries is an 8-byte field specifying the total number of tile entries (Run-Length is greater than 0).
A value of 0 indicates that the number is unknown.
This field is encoded as a little-endian 64-bit unsigned integer.
The Number of Tile Contents is an 8-byte field specifying the total number of blobs in the tile data section.
A value of 0 indicates that the number is unknown.
This field is encoded as a little-endian 64-bit unsigned integer.
Clustered is a 1-byte field specifying if the data of the individual tiles in the data section is ordered by their Tile-ID (clustered) or not (not clustered).
Therefore, Clustered means that offsets are either contiguous with the previous offset+length, or refer to a lesser offset when writing with deduplication.
The field can have one of the following values:
| Value | Meaning |
|---|---|
0x00 |
Not clustered |
0x01 |
Clustered |
The Internal Compression is a 1-byte field specifying the compression of the root directory, metadata, and all leaf directories.
The encoding of this field is described in Chapter 3.3.
The Tile Compression is a 1-byte field specifying the compression of all tiles.
The encoding of this field is described in Chapter 3.3.
The Tile Type is a 1-byte field specifying the type of tiles.
The field can have one of the following values:
| Value | Meaning |
|---|---|
0x00 |
Unknown / Other |
0x01 |
Mapbox Vector Tile |
0x02 |
PNG |
0x03 |
JPEG |
0x04 |
WebP |
0x05 |
AVIF |
The Min Zoom is a 1-byte field specifying the minimum zoom (LOD) of the tiles.
This field is encoded as an 8-bit unsigned integer.
The Max Zoom is a 1-byte field specifying the maximum zoom (LOD) of the tiles.
This field is encoded as an 8-bit unsigned integer.
The Min Position is an 8-byte field that includes the minimum latitude and minimum longitude of the bounds.
The encoding of this field is described in Chapter 3.4.
The Max Position is an 8-byte field including the maximum latitude and maximum longitude of the bounds.
The encoding of this field is described in Chapter 3.4.
The Center Zoom is a 1-byte field specifying the center zoom (LOD) of the tiles. A reader MAY use this as the initial zoom when displaying tiles from the PMTiles archive.
This field is encoded as an 8-bit unsigned integer.
The Center Position is an 8-byte field that includes the latitude and longitude of the center position. A reader MAY use this as the initial center position when displaying tiles from the PMTiles archive.
The encoding of this field is described in Chapter 3.4.
Compression is an enum with the following values:
| Value | Meaning |
|---|---|
0x00 |
Unknown |
0x01 |
None |
0x02 |
GZip |
0x03 |
Brotli |
0x04 |
ZStd |
A Position is encoded into 8 bytes. Bytes 0 through 3 (the first 4 bytes) represent the latitude, and bytes 4 through 7 (the last 4 bytes) represent the longitude.
To encode a latitude or a longitude into 4 bytes, use the following method:
- Multiply the value by 10,000,000.
- Convert the result into a little-endian 32-bit signed integer.
To decode a latitude or a longitude from 4 bytes, use the following method:
- Read bytes as a little-endian 32-bit signed integer.
- Divide the read value by 10,000,000.
A directory is simply a list of entries. Each entry describes either where a specific tile can be found in the tile data section or where a leaf directory can be found in the leaf directories section.
The number of entries in the root directory and in the leaf directories is left to the implementation and can vary drastically depending on what the writer has optimized for (cost, bandwidth, latency, etc.).
However, the size of the header plus the compressed size of the root directory MUST NOT exceed 16384 bytes to allow latency-optimized clients to retrieve the root directory in its entirety. Therefore, the maximum compressed size of the root directory is 16257 bytes (16384 bytes - 127 bytes). A sophisticated writer might need several attempts to optimize this.
Each directory entry consists of the following properties:
- Tile ID
- Offset
- Length
- Run-Length
Specifies the ID of the tile or the first tile in the leaf directory.
The Tile-ID corresponds to a cumulative position on the series of Hilbert curves starting at zoom level 0.
| Z | X | Y | TileID |
|---|---|---|---|
| 0 | 0 | 0 | 0 |
| 1 | 0 | 0 | 1 |
| 1 | 0 | 1 | 2 |
| 1 | 1 | 0 | 3 |
| 1 | 1 | 1 | 4 |
| 2 | 0 | 0 | 5 |
| ... | |||
| 12 | 3423 | 1763 | 19078479 |
Specifies the offset of the first byte of the tile or leaf directory. This address offset is relative to the first byte of the tile data section for tile-entries and relative to the first byte of the leaf directories section for leaf-directory-entries.
Specifies the number of bytes of this tile or leaf directory. This size always indicates the compressed size, if the tile or leaf directory is compressed.
Specifies the number of tiles for which this entry is valid. A run length of 0 means that this entry is for a leaf directory and not for a tile.
| Tile-ID | Offset | Length | Run-Length | Description |
|---|---|---|---|---|
5 |
1337 |
42 |
1 |
Tile 5 is located at bytes 1337–1378 of the tile data section. |
5 |
1337 |
42 |
3 |
Tiles 5, 6, and 7 are located at bytes 1337–1378 of the tile data section. |
5 |
1337 |
42 |
0 |
A leaf directory whose first tile has an ID of 5 is located at byte 1337–1378 of the leaf directories section. |
A directory can only be encoded in its entirety. It is not possible to encode a single directory entry by itself.
Appendix A.1 includes a pseudocode implementation of encoding a directory.
An encoded directory consists of five parts in the following order:
- The number of entries contained in the directory (MUST be greater than 0)
- Tile-IDs of all entries
- Run-Lengths of all entries
- Lengths of all entries
- Offsets of all entries
The number of entries included in this directory.
This field is encoded as a little-endian variable-width integer.
The Tile-IDs are delta-encoded, i.e., the number to be written is the difference to the last Tile-ID.
For example, the Tile-IDs 5, 42, and 69 would be encoded as 5 (5 - 0), 37 (42 - 5), and 27 (69 - 42).
Each delta-encoded Tile-ID is encoded as a little-endian variable-width integer.
The Run-Lengths are simply encoded as is, each as a little-endian variable-width integer.
The lengths are simply encoded as is, each as a little-endian variable-width integer. Each length MUST be greater than 0.
Offsets are encoded either as Offset + 1 or 0, if they are equal to the sum of offset and length of the previous entry (tile blobs are contiguous).
Each offset is encoded as a little-endian variable-width integer.
After encoding, each directory is compressed according to the internal compression field of the header. Leaf directories are compressed separately and not as a whole section.
Decoding a directory works similarly to encoding, but in reverse. Appendix A.2 includes a pseudocode implementation of decoding a directory. The basic steps are the following:
- Decompress the data according to the internal compression.
- Read a variable-width integer indicating how many entries are included in the directory (let's call this
n). - Read
nnumber of variable-width integers, which are the delta-encoded Tile IDs of all entries. ¹ - Read
nnumber of variable-width integers, which are the Run-Lenghts of all entries. - Read
nnumber of variable-width integers, which are the Lenghts of all entries. - Read
nnumber of variable-width integers, which are the Offsets of all entries. ¹
¹ Please refer to Section 4.2 for details on how Tile ID and Offset are encoded.
The meta data section MUST contain a valid JSON object encoded in UTF-8, which MAY include additional meta data related to the tileset that is not already covered in the header section.
If the Tile Type in the header has a value of Mapbox Vector Tile, the object SHOULD contain a key of vector_layers as described in the TileJSON 3.0 specification.
Additionally, this specification defines the following keys, which MAY be included in the object:
| Key | Description | Type |
|---|---|---|
name |
A name describing the tileset | string |
description |
A text description of the tileset | string |
attribution |
An attribution to be displayed when the map is shown to a user. Implementations MAY decide to treat this as HTML or literal text. | string |
type |
The type of the tileset | a string with a value of either overlay or baselayer |
version |
The version number of the tileset | a string containing a valid version according to Semantic Versioning 2.0.0 |
The JSON object MAY also include any other keys with an arbitrary value. This specification recommends nesting all application-specific data in an object under a semi-unique key to avoid overlap with other application-specific data or keys that may be defined in future versions of this specification. For example, instead of including the custom fields author and companyId directly in the top level of the metadata object, they SHOULD be nested in another object under a key with your project or organization name.
write_var_int(x, y) = write 'y' as a little-endian variable-width integer to 'x'
compress(x) = compress 'x' according to internal compression
entries = list of entries in this directory
buffer = the output byte-buffer
last_id = 0
for entry in entries {
write_var_int(buffer, entry.tile_id - last_id)
last_id = entry.tile_id
}
for entry in entries {
write_var_int(buffer, entry.run_length)
}
for entry in entries {
write_var_int(buffer, entry.length)
}
next_byte = 0
for (index, entry) in entries {
if index > 0 && entry.offset == next_byte {
write_var_int(buffer, 0)
} else {
write_var_int(buffer, entry.offset + 1)
}
next_byte = entry.offset + entry.length
}
compress(buffer)read_var_int(x) = read little-endian variable-width integer from 'x'
decompress(x) = decompress 'x' according to internal compression
input_buffer = the input byte-buffer
buffer = decompress(input_buffer)
num_entries = read_var_int(buffer)
entries = empty list of entries
last_id = 0
for i in num_entries {
value = read_var_int(buffer)
last_id = last_id + value
entries[i] = Entry { tile_id: last_id }
}
for i in num_entries {
entries[i].run_length = read_var_int(buffer)
}
for i in num_entries {
entries[i].length = read_var_int(buffer)
}
for i in num_entries {
value = read_var_int(buffer)
if value == 0 && i > 0 {
// offset = 0 -> entry is directly after previous entry
prev_entry = entries[i - 1];
entries[i].offset = prev_entry.offset + prev_entry.length;
} else {
entries[i].offset = value - 1;
}
}