# MBTiles

Starting with GDAL 1.10, the MBTiles driver allows reading rasters in the MBTiles format, which is a specification for storing tiled map data in SQLite databases.

Starting with GDAL 2.1, the MBTiles driver has creation and write support for MBTiles raster datasets.

Starting with GDAL 2.3, the MBTiles driver has read and write support for MBTiles vector datasets. For standalone Mapbox Vector Tile files or set of MVT files, see the MVT driver. Note: vector write support requires GDAL to be built with GEOS.

GDAL/OGR must be compiled with OGR SQLite driver support, and JPEG and PNG drivers.

The SRS is always the Pseudo-Mercator (a.k.a Google Mercator) projection.

Starting with GDAL 2.3, the driver will open a dataset as RGBA. For previous versions, the driver will try to determine the number of bands by probing the content of one tile. It is possible to alter this behaviour by defining the MBTILES_BAND_COUNT configuration option (or starting with GDAL 2.1, the BAND_COUNT open option) to the number of bands. The values supported are 1, 2, 3 or 4. Four band (Red,Green,Blue,Alpha) dataset gives the maximum compatibility with the various encodings of tiles that can be stored.

The driver will use the 'bounds' metadata in the metadata table and do necessary tile clipping, if needed, to respect that extent. However that information being optional, if omitted, the driver will use the extent of the tiles at the maximum zoom level. The user can also specify the USE_BOUNDS=NO open option to force the use of the actual extent of tiles at the maximum zoom level. Or it can specify any of MINX/MINY/MAXX/MAXY to have a custom extent.

The driver can retrieve pixel attributes encoded according to the UTFGrid specification available in some MBTiles files. They can be obtained with the gdallocationinfo utility, or with a GetMetadataItem("Pixel_iCol_iLine", "LocationInfo") call on a band object.

## Opening options

Starting with GDAL 2.1, the following open options are available:

- Raster and vector:
  - ZOOM_LEVEL=value: Integer value between 0 and the maximum filled in the tiles table. By default, the driver will select the maximum zoom level, such as at least one tile at that zoom level is found in the 'tiles' table.
  - USE_BOUNDS=YES/NO: Whether to use the 'bounds' metadata, when available, to determine the AOI. Defaults to YES.
  - MINX=value: Minimum easting (in EPSG:3857) of the area of interest.
  - MINY=value: Minimum northing (in EPSG:3857) of the area of interest.
  - MAXX=value: Maximum easting (in EPSG:3857) of the area of interest.
  - MAXY=value: Maximum northing (in EPSG:3857) of the area of interest.
- Raster only:
  - BAND_COUNT=AUTO/1/2/3/4: Number of bands of the dataset exposed after opening. Some conversions will be done when possible and implemented, but this might fail in some cases, depending on the BAND_COUNT value and the number of bands of the tile. Defaults to AUTO.
  - TILE_FORMAT=PNG/PNG8/JPEG: Format used to store tiles. See Tile formats section. Only used in update mode. Defaults to PNG.
  - QUALITY=1-100: Quality setting for JPEG compression. Only used in update mode. Default to 75.
  - ZLEVEL=1-9: DEFLATE compression level for PNG tiles. Only used in update mode. Default to 6.
  - DITHER=YES/NO: Whether to use Floyd-Steinberg dithering (for TILE_FORMAT=PNG8). Only used in update mode. Defaults to NO.
- Vector only (GDAL >= 2.3):
  - CLIP=YES/NO: Whether to clip geometries of vector features to tile extent. Defaults to YES.
  - ZOOM_LEVEL_AUTO=YES/NO: Whether to auto-select the zoom level for vector layers according to the spatial filter extent. Only for display purpose. Defaults to NO.
  JSON_FIELD=YES/NO: Whether to put all attributes as a serialized JSon dictionary.

## Raster creation issues

Depending of the number of bands of the input dataset and the tile format selected, the driver will do the necessary conversions to be compatible with the tile format. When using the CreateCopy() API (such as with gdal_translate), automatic reprojection of the input dataset to EPSG:3857 (WebMercator) will be done, with selection of the appropriate zoom level.

Fully transparent tiles will not be written to the database, as allowed by the format.

The driver implements the Create() and IWriteBlock() methods, so that arbitrary writing of raster blocks is possible, enabling the direct use of MBTiles as the output dataset of utilities such as gdalwarp.

On creation, raster blocks can be written only if the geotransformation matrix has been set with SetGeoTransform() This is effectively needed to determine the zoom level of the full resolution dataset based on the pixel resolution, dataset and tile dimensions.

Technical/implementation note: in the general case, GDAL blocks do not exactly match a single MBTiles tile. In which case, each GDAL block will overlap four MBTiles tiles. This is easily handled on the read side, but on creation/update side, such configuration could cause numerous decompression/ recompression of tiles to be done, which might cause unnecessary quality loss when using lossy compression (JPEG). To avoid that, the driver will create a temporary database next to the main MBTiles file to store partial MBTiles tiles in a lossless (and uncompressed) way. Once a tile has received data for its four quadrants and for all the bands (or the dataset is closed or explicitly flushed with FlushCache()), those uncompressed tiles are definitely transferred to the MBTiles file with the appropriate compression. All of this is transparent to the user of GDAL API/utilities

### Tile formats

MBTiles can store tiles in PNG or JPEG. Support for those tile formats depend if the underlying drivers are available in GDAL. By default, GDAL will PNG tiles.

It is possible to select the tile format by setting the creation/open option TILE_FORMAT to one of PNG, PNG8 or JPEG. When using JPEG, the alpha channel will not be stored.

PNG8 can be selected to use 8-bit PNG with a color table up to 256 colors. On creation, an optimized color table is computed for each tile. The DITHER option can be set to YES to use Floyd/Steinberg dithering algorithm, which spreads the quantization error on neighbouring pixels for better rendering (note however than when zooming in, this can cause non desirable visual artifacts). Setting it to YES will generally cause less effective compression. Note that at that time, such an 8-bit PNG formulation is only used for fully opaque tiles, as the median-cut algorithm currently implemented to compute the optimal color table does not support alpha channel (even if PNG8 format would potentially allow color table with transparency). So when selecting PNG8, non fully opaque tiles will be stored as 32-bit PNG.

## Vector creation issues

Tiles are generated with WebMercator (EPSG:3857) projection. Several layers can be written. It is possible to decide at which zoom level ranges a given layer is written.

## Creation options

The following creation options are available:

- Raster and vector:
  - NAME=string. Tileset name, used to set the 'name' metadata item. If not specified, the basename of the filename will be used.
  - DESCRIPTION=string. A description of the layer, used to set the 'description' metadata item. If not specified, the basename of the filename will be used.
  - TYPE=overlay/baselayer. The layer type, used to set the 'type' metadata item. Default to 'overlay'.
- Raster only:
  - VERSION=string. The version of the tileset, as a plain number, used to set the 'version' metadata item. Default to '1.1'.
  - BLOCKSIZE=integer. (GDAL >= 2.3) Block/tile size in width and height in pixels. Defaults to 256. Maximum supported is 4096.
  - TILE_FORMAT=PNG/PNG8/JPEG: Format used to store tiles. See Tile formats section. Defaults to PNG.
  - QUALITY=1-100: Quality setting for JPEG compression. Default to 75.
  - ZLEVEL=1-9: DEFLATE compression level for PNG tiles. Default to 6.
  - DITHER=YES/NO: Whether to use Floyd-Steinberg dithering (for TILE_FORMAT=PNG8). Defaults to NO.
  - ZOOM_LEVEL_STRATEGY=AUTO/LOWER/UPPER. Strategy to determine zoom level. LOWER will select the zoom level immediately below the theoretical computed non-integral zoom level, leading to subsampling. On the contrary, UPPER will select the immediately above zoom level, leading to oversampling. Defaults to AUTO which selects the closest zoom level.
  - RESAMPLING=NEAREST/BILINEAR/CUBIC/CUBICSPLINE/LANCZOS/MODE/AVERAGE. Resampling algorithm. Defaults to BILINEAR.
  - WRITE_BOUNDS=YES/NO: Whether to write the bounds 'metadata' item. Defaults to YES.
- Vector only (GDAL >= 2.3):
  - MINZOOM=integer: Minimum zoom level at which tiles are generated. Defaults to 0.
  - MAXZOOM=integer: Minimum zoom level at which tiles are generated. Defaults to 5. Maximum supported value is 22
  - CONF=string: Layer configuration as a JSon serialized string.
  - SIMPLIFICATION=float: Simplification factor for linear or polygonal geometries. The unit is the integer unit of tiles after quantification of geometry coordinates to tile coordinates. Applies to all zoom levels, unless SIMPLIFICATION_MAX_ZOOM is also defined.
  - SIMPLIFICATION_MAX_ZOOM=float: Simplification factor for linear or polygonal geometries, that applies only for the maximum zoom level.
  - EXTENT=positive_integer. Number of units in a tile. The greater, the more accurate geometry coordinates (at the expense of tile byte size). Defaults to 4096
  - BUFFER=positive_integer. Number of units for geometry buffering. This value corresponds to a buffer around each side of a tile into which geometries are fetched and clipped. This is used for proper rendering of geometries that spread over tile boundaries by some rendering clients. Defaults to 80 if EXTENT=4096.
  - COMPRESS=YES/NO. Whether to compress tiles with the Deflate/GZip algorithm. Defaults to YES. Should be left to YES for FORMAT=MBTILES.
  - TEMPORARY_DB=string. Filename with path for the temporary database used for tile generation. By default, this will be a file in the same directory as the output file/directory.
  - MAX_SIZE=integer. Maximum size of a tile in bytes (after compression). Defaults to 500 000. If a tile is greater than this threshold, features will be written with reduced precision, or discarded.
  - MAX_FEATURES=integer. Maximum number of features per tile. Defaults to 200 000.
  - BOUNDS=min_long,min_lat,max_long,max_lat. Override default value for bounds metadata item which is computed from the extent of features written.
  - CENTER=long,lat,zoom_level. Override default value for center metadata item, which is the center of BOUNDS at minimum zoom level.

## Layer configuration (vector)

The above mentioned CONF dataset creation option can be set to a string whose value is a JSon serialized document such as the below one:

            {
                "boundaries_lod0": {
                    "target_name": "boundaries",
                    "description": "Country boundaries",
                    "minzoom": 0,
                    "maxzoom": 2
                },
                "boundaries_lod1": {
                    "target_name": "boundaries",
                    "minzoom": 3,
                    "maxzoom": 5
                }
            }

boundaries_lod0 and boundaries_lod1 are the name of the OGR layers that are created into the target MVT dataset. They are mapped to the MVT target layer boundaries.

It is also possible to get the same behaviour with the below layer creation options, although that is not convenient in the ogr2ogr use case.

## Layer creation options (vector)

- MINZOOM=integer: Minimum zoom level at which tiles are generated. Defaults to the dataset creation option MINZOOM value.
- MAXZOOM=integer: Minimum zoom level at which tiles are generated. Defaults to the dataset creation option MAXZOOM value. Maximum supported value is 22
- NAME=string: Target layer name. Defaults to the layer name, but can be overridden so that several OGR layers map to a single target MVT layer. The typical use case is to have different OGR layers for mutually exclusive zoom level ranges.
- DESCRIPTION=string: A description of the layer.

## Overviews (raster)

gdaladdo / BuildOverviews() can be used to compute overviews. Only power-of-two overview factors (2,4,8,16,...) are supported.

If more overview levels are specified than available, the extra ones are silently ignored.

Overviews can also be cleared with the -clean option of gdaladdo (or BuildOverviews() with nOverviews=0)

## Vector tiles

Starting with GDAL 2.3, the MBTiles driver can read MBTiles files containing vector tiles conforming to the Mapbox Vector Tile format (format=pbf).

The driver requires the 'metadata' table to contain a name='json' entry, that has a 'vector_layers' array describing layers and their schema. See metadata.json

Note: The driver will make no effort of stiching together geometries for features that overlap several tiles.

## Examples:

- Accessing a remote MBTiles raster :

      $ gdalinfo /vsicurl/http://a.tiles.mapbox.com/v3/kkaefer.iceland.mbtiles

  Output:

      Driver: MBTiles/MBTiles
      Files: /vsicurl/http://a.tiles.mapbox.com/v3/kkaefer.iceland.mbtiles
      Size is 16384, 16384
      Coordinate System is:
      PROJCS["WGS 84 / Pseudo-Mercator",
          GEOGCS["WGS 84",
              DATUM["WGS_1984",
                  SPHEROID["WGS 84",6378137,298.257223563,
                      AUTHORITY["EPSG","7030"]],
                  AUTHORITY["EPSG","6326"]],
              PRIMEM["Greenwich",0,
                  AUTHORITY["EPSG","8901"]],
              UNIT["degree",0.0174532925199433,
                  AUTHORITY["EPSG","9122"]],
              AUTHORITY["EPSG","4326"]],
          PROJECTION["Mercator_1SP"],
          PARAMETER["central_meridian",0],
          PARAMETER["scale_factor",1],
          PARAMETER["false_easting",0],
          PARAMETER["false_northing",0],
          UNIT["metre",1,
              AUTHORITY["EPSG","9001"]],
          AXIS["X",EAST],
          AXIS["Y",NORTH],
          EXTENSION["PROJ4","+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs"],
          AUTHORITY["EPSG","3857"]]
      Origin = (-3757031.250000000000000,11271093.750000000000000)
      Pixel Size = (152.873992919921875,-152.873992919921875)
      Image Structure Metadata:
        INTERLEAVE=PIXEL
      Corner Coordinates:
      Upper Left  (-3757031.250,11271093.750) ( 33d44'59.95"W, 70d36'45.36"N)
      Lower Left  (-3757031.250, 8766406.250) ( 33d44'59.95"W, 61d36'22.97"N)
      Upper Right (-1252343.750,11271093.750) ( 11d14'59.98"W, 70d36'45.36"N)
      Lower Right (-1252343.750, 8766406.250) ( 11d14'59.98"W, 61d36'22.97"N)
      Center      (-2504687.500,10018750.000) ( 22d29'59.97"W, 66d30'47.68"N)
      Band 1 Block=256x256 Type=Byte, ColorInterp=Red
        Overviews: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
        Mask Flags: PER_DATASET ALPHA
        Overviews of mask band: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
      Band 2 Block=256x256 Type=Byte, ColorInterp=Green
        Overviews: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
        Mask Flags: PER_DATASET ALPHA
        Overviews of mask band: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
      Band 3 Block=256x256 Type=Byte, ColorInterp=Blue
        Overviews: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
        Mask Flags: PER_DATASET ALPHA
        Overviews of mask band: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512
      Band 4 Block=256x256 Type=Byte, ColorInterp=Alpha
        Overviews: 8192x8192, 4096x4096, 2048x2048, 1024x1024, 512x512

- Reading pixel attributes encoded according to the UTFGrid specification :

      $ gdallocationinfo /vsicurl/http://a.tiles.mapbox.com/v3/mapbox.geography-class.mbtiles -wgs84 2 49 -b 1 -xml

  Output:

      <Report pixel="33132" line="22506">
        <BandReport band="1">
          <LocationInfo>
            <Key>74</Key>
            <JSon>{"admin":"France","flag_png":" "}</JSon>
          </LocationInfo>
          <Value>238</Value>
        </BandReport>
      </Report>

- Converting a dataset to MBTiles and adding overviews :

      $ gdal_translate my_dataset.tif my_dataset.mbtiles -of MBTILES
      $ gdaladdo -r average my_dataset.mbtiles 2 4 8 16

- Opening a vector MBTiles:

      $ ogrinfo /home/even/gdal/data/mvt/out.mbtiles
      INFO: Open of `/home/even/gdal/data/mvt/out.mbtiles'
            using driver `MBTiles' successful.
      Metadata:
        ZOOM_LEVEL=5
        name=out.mbtiles
        description=out.mbtiles
        version=2
        minzoom=0
        maxzoom=5
        center=16.875000,44.951199,5
        bounds=-180.000000,-85.051129,180.000000,83.634101
        type=overlay
        format=pbf
      1: ne_10m_admin_1_states_provinces_shpgeojson (Multi Polygon)

- Converting a GeoPackage to a Vector tile MBTILES:

      $ ogr2ogr -f MBTILES target.mbtiles source.gpkg -dsco MAXZOOM=10

See Also:

- MBTiles specification
- UTFGrid specification
- Mapbox Vector tiles driver