drivers/vector/csv.rst

.. _vector.csv:

Comma Separated Value (.csv)
============================

.. shortname:: CSV

.. built_in_by_default::

OGR supports reading and writing primarily non-spatial tabular data
stored in text CSV files. CSV files are a common interchange format
between software packages supporting tabular data and are also easily
produced manually with a text editor or with end-user written scripts or
programs.

While in theory .csv files could have any extension, in order to
auto-recognise the format OGR only supports CSV files ending with the
extension ".csv". The datasource name may be either a single CSV file or
point to a directory. For a directory to be recognised as a .csv
datasource at least half the files in the directory need to have the
extension .csv. One layer (table) is produced from each .csv file
accessed.

For files structured as CSV, but not ending
with .CSV extension, the 'CSV:' prefix can be added before the filename
to force loading by the CSV driver.

The OGR CSV driver supports reading and writing. Because the CSV format
has variable length text lines, reading is done sequentially. Reading
features in random order will generally be very slow. OGR CSV layer
might have a coordinate system stored in a .prj file (see GeoCSV
specification). When reading a field named "WKT" is assumed to contain
WKT geometry, but also is treated as a regular field. The OGR CSV driver
returns all attribute columns as string data types if no field type
information file (with .csvt extension) is available.

Limited type recognition can be done for Integer, Real, String, Date
(YYYY-MM-DD), Time (HH:MM:SS+nn), DateTime (YYYY-MM-DD HH:MM:SS+nn)
columns through a descriptive file with the same name as the CSV file,
but a .csvt extension. In a single line the types for each column have
to be listed with double quotes and be comma separated (e.g.,
"Integer","String"). It is also possible to specify explicitly the width
and precision of each column, e.g.
"Integer(5)","Real(10.7)","String(15)". The driver will then use these
types as specified for the csv columns. Subtypes
can be passed between parenthesis, such as "Integer(Boolean)",
"Integer(Int16)" and "Real(Float32)". Starting with GDAL 2.1,
accordingly with the `GeoCSV
specification <http://giswiki.hsr.ch/GeoCSV>`__, the "CoordX" or
"Point(X)" type can be used to specify a column with longitude/easting
values, "CoordY" or "Point(Y)" for latitude/northing values and "WKT"
for geometries encoded in WKT

Starting with GDAL 2.2, the "JSonStringList", "JSonIntegerList",
"JSonInteger64List" and "JSonRealList" types can be used in .csvt to map
to the corresponding OGR StringList, IntegerList, Integer64List and
RealList types. The field values are then encoded as JSon arrays, with
proper CSV escaping.

Automatic field type guessing can also be done
if specifying the open options described in the below "Open options"
section.

Driver capabilities
-------------------

.. supports_create::

.. supports_georeferencing::

.. supports_virtualio::

Format
------

CSV files have one line for each feature (record) in the layer (table).
The attribute field values are separated by commas. At least two fields
per line must be present. Lines may be terminated by a DOS (CR/LF) or
Unix (LF) style line terminators. Each record should have the same
number of fields. The driver will also accept a semicolon, a tabulation
or a space character as field separator .
This autodetection will work only if there's no other potential
separator on the first line of the CSV file. Otherwise it will default
to comma as separator.

Complex attribute values (such as those containing commas, quotes or
newlines) may be placed in double quotes. Any occurrences of double
quotes within the quoted string should be doubled up to "escape" them.

By default, the driver attempts to treat the first line of the file as a
list of field names for all the fields. However, if one or more of the
names is all numeric it is assumed that the first line is actually data
values and dummy field names are generated internally (field_1 through
field_n) and the first record is treated as a feature.
Numeric values are treated as field names if they are
enclosed in double quotes. Starting with GDAL 2.1, this behavior can be
modified via the HEADERS open option.

All CSV files are treated as UTF-8 encoded. A
Byte Order Mark (BOM) at the beginning of the file will be parsed
correctly. The option WRITE_BOM can be used to create a file
with a Byte Order Mark, which can improve compatibility with some
software (particularly Excel).

Example (employee.csv):

::

   ID,Salary,Name,Comments
   132,55000.0,John Walker,"The ""big"" cheese."
   133,11000.0,Jane Lake,Cleaning Staff

Note that the Comments value for the first data record is placed in
double quotes because the value contains quotes, and those quotes have
to be doubled up so we know we haven't reached the end of the quoted
string yet.

Many variations of textual input are sometimes called Comma Separated
Value files, including files without commas, but fixed column widths,
those using tabs as separators or those with other auxiliary data
defining field types or structure. This driver does not attempt to
support all such files, but instead to support simple .csv files that
can be auto-recognised. Scripts or other mechanisms can generally be
used to convert other variations into a form that is compatible with the
OGR CSV driver.

Reading CSV containing spatial information
------------------------------------------

Building point geometries
~~~~~~~~~~~~~~~~~~~~~~~~~

Consider the following CSV file (test.csv):

::

   Latitude,Longitude,Name
   48.1,0.25,"First point"
   49.2,1.1,"Second point"
   47.5,0.75,"Third point"

Starting with GDAL 2.1, it is possible to directly specify the potential
names of the columns that can contain X/longitude and Y/latitude with
the X_POSSIBLE_NAMES and Y_POSSIBLE_NAMES open option.

*ogrinfo -ro -al test.csv -oo X_POSSIBLE_NAMES=Lon\* -oo
Y_POSSIBLE_NAMES=Lat\* -oo KEEP_GEOM_COLUMNS=NO* will return :

::

   OGRFeature(test):1
     Name (String) = First point
     POINT (0.25 48.1)

   OGRFeature(test):2
     Name (String) = Second point
     POINT (1.1 49.2)

   OGRFeature(test):3
     Name (String) = Third point
     POINT (0.75 47.5)

If CSV file does not have a header line, the dummy "field_n" names can be
used as possible names for coordinate fields. For example plain XYZ point
data can be opened as

*ogrinfo -ro -al elevation.xyz -oo X_POSSIBLE_NAMES=field_1 -oo
Y_POSSIBLE_NAMES=field_2 -oo Z_POSSIBLE_NAMES=field_3*

Otherwise, if one or several columns contain a geometry definition
encoded as WKT, WKB (encoded in hexadecimal) or GeoJSON (in which case
the GeoJSON content must be formatted to follow CSV rules, that is to
say it must be surrounded by double-quotes, and double-quotes inside the
string must be repeated for proper escaping), the name of such column(s)
the GEOM_POSSIBLE_NAMES open option.

For older versions, it is possible to extract spatial information
(points) from a CSV file which has columns for the X and Y coordinates,
through the use of the :ref:`VRT <vector.vrt>` driver.

You can write the associated VRT file (test.vrt):

::

   <OGRVRTDataSource>
       <OGRVRTLayer name="test">
           <SrcDataSource>test.csv</SrcDataSource>
           <GeometryType>wkbPoint</GeometryType>
           <LayerSRS>WGS84</LayerSRS>
           <GeometryField encoding="PointFromColumns" x="Longitude" y="Latitude"/>
       </OGRVRTLayer>
   </OGRVRTDataSource>

and *ogrinfo -ro -al test.vrt* will return :

::

   OGRFeature(test):1
     Latitude (String) = 48.1
     Longitude (String) = 0.25
     Name (String) = First point
     POINT (0.25 48.1 0)

   OGRFeature(test):2
     Latitude (String) = 49.2
     Longitude (String) = 1.1
     Name (String) = Second point
     POINT (1.1 49.200000000000003 0)

   OGRFeature(test):3
     Latitude (String) = 47.5
     Longitude (String) = 0.75
     Name (String) = Third point
     POINT (0.75 47.5 0)

Building line geometries
~~~~~~~~~~~~~~~~~~~~~~~~

Consider the following CSV file (test.csv):

::

   way_id,pt_id,x,y
   1,1,2,49
   1,2,3,50
   2,1,-2,49
   2,2,-3,50

With a GDAL build with Spatialite enabled, *ogrinfo test.csv -dialect
SQLite -sql "SELECT way_id, MakeLine(MakePoint(CAST(x AS float),CAST(y
AS float))) FROM test GROUP BY way_id"* will return :

::

   OGRFeature(SELECT):0
     way_id (String) = 1
     LINESTRING (2 49,3 50)

   OGRFeature(SELECT):1
     way_id (String) = 2
     LINESTRING (-2 49,-3 50)

Open options
------------

The following open options can be specified
(typically with the -oo name=value parameters of ogrinfo or ogr2ogr):

-  **MERGE_SEPARATOR**\ =YES/NO (defaults to NO). Setting it to YES will
   enable merging consecutive separators. Mostly useful when it is the
   space character.
-  **AUTODETECT_TYPE**\ =YES/NO (defaults to NO). Setting it to YES will
   enable auto-detection of field data types. If while reading the
   records (beyond the records used for autodetection), a value is found
   to not correspond to the autodetected data type, a warning will be
   emitted and the field will be emptied.
-  **KEEP_SOURCE_COLUMNS**\ =YES/NO (default NO) keep a copy of the
   original columns where the guessing is active, and the guessed type
   is different from string. The name of the original columns will be
   suffixed with "_original". This flag should be used only when
   AUTODETECT_TYPE=YES.
-  **AUTODETECT_WIDTH**\ =YES/NO/STRING_ONLY (defaults to NO). Setting
   it to YES to detect the width of string and integer fields, and the
   width and precision of real fields. Setting it to STRING_ONLY
   restricts to string fields. Setting it to NO select default size and
   width. If while reading the records (beyond the records used for
   autodetection), a value is found to not correspond to the
   autodetected width/precision, a warning will be emitted and the field
   will be emptied.
-  **AUTODETECT_SIZE_LIMIT**\ =size to specify the number of bytes to
   inspect to determine the data type and width/precision. The default
   will be 100000. Setting 0 means inspecting the whole file. Note :
   specifying a value over 1 MB (or 0 if the file is larger than 1MB)
   will prevent reading from standard input.
-  **QUOTED_FIELDS_AS_STRING**\ =YES/NO (default NO). Only used if
   AUTODETECT_TYPE=YES. Whether to enforce quoted fields as string
   fields when set to YES. Otherwise, by default, the content of quoted
   fields will be tested for real, integer, etc... data types.
-  **X_POSSIBLE_NAMES**\ =list_of_names. (GDAL >= 2.1) Comma separated
   list of possible names for X/longitude coordinate of a point. Each
   name might be a pattern using the star character in starting and/or
   ending position. E.g.: prefix*, \*suffix or \*middle*. The values in
   the column must be floating point values. X_POSSIBLE_NAMES and
   Y_POSSIBLE_NAMES must be both specified and a matching for each must
   be found in the columns of the CSV file. Only one geometry column per
   layer might be built when using X_POSSIBLE_NAMES/Y_POSSIBLE_NAMES.
-  **Y_POSSIBLE_NAMES**\ =list_of_names. (GDAL >= 2.1) Comma separated
   list of possible names for Y/latitude coordinate of a point. Each
   name might be a pattern using the star character in starting and/or
   ending position. E.g.: prefix*, \*suffix or \*middle*. The values in
   the column must be floating point values. X_POSSIBLE_NAMES and
   Y_POSSIBLE_NAMES must be both specified and a matching for each must
   be found in the columns of the CSV file.
-  **Z_POSSIBLE_NAMES**\ =list_of_names. (GDAL >= 2.1) Comma separated
   list of possible names for Z/elevation coordinate of a point. Each
   name might be a pattern using the star character in starting and/or
   ending position. E.g.: prefix*, \*suffix or \*middle*. The values in
   the column must be floating point values. Only taken into account in
   combination with X_POSSIBLE_NAMES and Y_POSSIBLE_NAMES.
-  **GEOM_POSSIBLE_NAMES**\ =list_of_names. (GDAL >= 2.1) Comma
   separated list of possible names for geometry columns that contain
   geometry definitions encoded as WKT, WKB (in hexadecimal form,
   potentially in PostGIS 2.0 extended WKB) or GeoJSON. Each name might
   be a pattern using the star character in starting and/or ending
   position. E.g.: prefix*, \*suffix or \*middle\*
-  **KEEP_GEOM_COLUMNS**\ =YES/NO (default YES) Expose the detected
   X,Y,Z or geometry columns as regular attribute fields.
-  **HEADERS**\ =YES/NO/AUTO (default AUTO) (GDAL >= 2.1) Whether the
   first line of the file contains column names or not. When set to
   AUTO, GDAL will assume the first line is column names if none of the
   values are strictly numeric.
-  **EMPTY_STRING_AS_NULL**\ =YES/NO (default NO) (GDAL >= 2.1) Whether
   to consider empty strings as null fields on reading'.

Creation Issues
---------------

The driver supports creating new databases (as a directory of .csv
files), adding new .csv files to an existing directory or .csv files or
appending features to an existing .csv table. Starting with GDAL 2.1,
deleting or replacing existing features, or adding/modifying/deleting
fields is supported, provided the modifications done are small enough to
be stored in RAM temporarily before flushing to disk.

Layer Creation options:

-  **LINEFORMAT**: By default when creating new .csv files they are
   created with the line termination conventions of the local platform
   (CR/LF on win32 or LF on all other systems). This may be overridden
   through use of the LINEFORMAT layer creation option which may have a
   value of **CRLF** (DOS format) or **LF** (Unix format).
-  **GEOMETRY**: By default, the geometry of
   a feature written to a .csv file is discarded. It is possible to
   export the geometry in its WKT representation by specifying
   GEOMETRY=\ **AS_WKT**. It is also possible to export point geometries
   into their X,Y,Z components (different columns in the csv file) by
   specifying GEOMETRY=\ **AS_XYZ**, GEOMETRY=\ **AS_XY** or
   GEOMETRY=\ **AS_YX**. The geometry column(s) will be prepended to the
   columns with the attributes values. It is also possible to export
   geometries in GeoJSON representation using SQLite SQL dialect query,
   see example below.
-  **CREATE_CSVT**\ =YES/NO: Create the
   associated .csvt file (see above paragraph) to describe the type of
   each column of the layer and its optional width and precision.
   Default value : NO
-  **SEPARATOR**\ =COMMA/SEMICOLON/TAB/SPACE:
   Field separator character. Default value : COMMA
-  **WRITE_BOM**\ =YES/NO: Write a UTF-8 Byte
   Order Mark (BOM) at the start of the file. Default value : NO
-  **GEOMETRY_NAME**\ =name (Starting with GDAL 2.1): Name of geometry
   column. Only used if GEOMETRY=AS_WKT and CREATE_CSVT=YES. Defaults to
   WKT
-  **STRING_QUOTING**\ =IF_NEEDED/IF_AMBIGUOUS/ALWAYS (Starting with
   GDAL 2.3): whether to double-quote strings. IF_AMBIGUOUS means that
   string values that look like numbers will be quoted (it also implies
   IF_NEEDED). Defaults to IF_AMBIGUOUS (behavior in older versions was
   IF_NEEDED)

Configuration options (set with ``--config key value`` on command line
utilities):

-  **OGR_WKT_PRECISION**\ =int: Number of decimals for coordinate
   values. Default to 15. A heuristics is used to remove insignificant
   trailing 00000x or 99999x that can appear when formatting decimal
   numbers.
-  **OGR_WKT_ROUND**\ =YES/NO: (GDAL >= 2.3) Whether to enable the above
   mentioned heuristics to remove insignificant trailing 00000x or
   99999x. Default to YES.

VSI Virtual File System API support
-----------------------------------

The driver supports reading and writing to files managed by VSI Virtual
File System API, which include "regular" files, as well as files in the
/vsizip/ (read-write) , /vsigzip/ (read-only) , /vsicurl/ (read-only)
domains.

Writing to /dev/stdout or /vsistdout/ is also supported.

Examples
~~~~~~~~

-  This example shows using ogr2ogr to transform a shapefile with point
   geometry into a .csv file with the X,Y,Z coordinates of the points as
   first columns in the .csv file

   ::

      ogr2ogr -f CSV output.csv input.shp -lco GEOMETRY=AS_XYZ

-  This example shows using ogr2ogr to transform a shapefile into a .csv
   file with geography field formatted using GeoJSON format.

   ::

      ogr2ogr -f CSV -dialect sqlite -sql "select AsGeoJSON(geometry) AS geom, * from input" output.csv input.shp

- Convert a CSV into a GeoPackage. Specify the names of the coordinate columns and assign a coordinate reference system.

   ::

     ogr2ogr \
       -f GPKG output.gpkg \
       input.csv \
       -oo X_POSSIBLE_NAMES=longitude \
       -oo Y_POSSIBLE_NAMES=latitude \
       -a_srs 'EPSG:4326'


Particular datasources
----------------------

The CSV driver can also read files whose structure is close to CSV files
:

-  Airport data files NfdcFacilities.xls, NfdcRunways.xls,
   NfdcRemarks.xls and NfdcSchedules.xls found on that `FAA
   website <http://www.faa.gov/airports/airport_safety/airportdata_5010/menu/index.cfm>`__

-  Files from the `USGS
   GNIS <http://geonames.usgs.gov/domestic/download_data.htm>`__
   (Geographic Names Information System)

-  The allCountries file from `GeoNames <http://www.geonames.org>`__

-  `Eurostat .TSV
   files <http://epp.eurostat.ec.europa.eu/NavTree_prod/everybody/BulkDownloadListing?file=read_me.pdf>`__

Other Notes
-----------

-  `GeoCSV specification <http://giswiki.hsr.ch/GeoCSV>`__ (supported by
   GDAL >= 2.1)
-  Initial development of the OGR CSV driver was supported by `DM
   Solutions Group <http://www.dmsolutions.ca/>`__ and
   `GoMOOS <http://www.gomoos.org/>`__.
-  `Carto <https://carto.com/>`__ funded field type auto-detection and
   open options related to geometry columns.