# NextGIS Web

NextGIS Web - is a server GIS, which allows to store and edit geodata and to display maps in web browser. Also NextGIS Web can share geodata with other NextGIS software.

NextGIS Web has the following features:

- Display maps in a web browser (different maps with different layers and styles)
- Flexible permissions management
- Load geodata from PostGIS or import from GIS formats (ESRI Shape, GeoJSON or GeoTIFF)
- Load vector geodata in the following formats: GeoJSON, CSV, ESRI Shape
- Import map styles from QGIS project or set them manually
- Act as a server for TMS, WMS, WFS
- Act as a client for WMS
- User can add photos to records, change record attributes via web interface or WFS-T protocol

NextGIS Web - is an open source software (license GPL v2+, see GNU General Public License, version 2).

## Driver

The driver is available since GDAL/OGR >= 2.4. This driver can connect to the services implementing the NextGIS Web API. GDAL/OGR must be built with Curl support in order for the NGW driver to be compiled. The driver supports read and write operations.

## Dataset name syntax

The minimal syntax to open a NGW datasource is: NGW:[NextGIS Web URL][/resource/][resource identifier]

- NextGIS Web URL may be an url to nextgis.com cloud service (for example, https://demo.nextgis.com), or some other url including port and additional path (for example, http://192.168.1.1:8000/test).
- resource is mandatory keyword dividing resource identifier from the rest of URL.
- resource identifier this is positive number from 0 and above. This may be a resource group, vector, PostGIS or raster layer, style.

If identifier is resource group, all vector layers, PostGIS, raster layers, styles will listed as child resources. In other case this will be a separate layer.

## Configuration options

The following configuration options are available:

- NGW_USERPWD: User name and password separated with colon. Optional and can be set using open options.
- NGW_BATCH_MODE: If set to YES - all edits (insert, update) will cache and execute if cache limit exceeded or sync to disk execute. Delete operation will execute immediately.
- NGW_PAGE_SIZE: If supported by server, fetch features from remote server will use paging. The -1 value disables paging even it supported by server.

## Authentication

Any operations (read, write, get metadata, change properties, etc.) may require an authenticated access. Authenticated access is obtained by specifying user name and password in open, create or configuration options.

## Geometry

NextGIS Web supports only one geometry column. Default spatial reference is Web Mercator (EPSG:3857). The following geometry types are available:

- POINT
- LINESTRING
- POLYGON
- MULTIPOINT
- MULTILINESTRING
- MULTIPOLYGON

## Field data types

NextWeb supports only following field types:

- OFTInteger
- OFTInteger64
- OFTReal
- OFTString
- OFTDate
- OFTTime
- OFTDateTime

## Paging

Features are retrieved from the server by chunks if server support this feature. This number can be altered with the NGW_PAGE_SIZE configuration option or PAGE_SIZE open option.

## Write support

Datasource and layers creation and deletion is possible. Write support is only enabled when the datasource is opened in update mode and user has permissions. Vector and PostGIS layers insert and update operations may be cached if BATCH_MODE is enable. Delete operation executes immediately.

## Open options

The following open options are available:

- USERPWD - Username and password, separated by colon.
- PAGE_SIZE=-1 - Limit feature count while fetching from server. Default value is -1 - no limit.
- BATCH_SIZE=-1 - Size of feature insert and update operations cache before send to server. If batch size is -1 batch mode is disabled. Default value is -1.

## Dataset creation options

The following dataset/datasource creation options are available:

- KEY - Key value. Must be unique in whole NextGIS Web instance. Optional.
- DESCRIPTION - Resource description. Optional.
- USERPWD - Username and password, separated by colon.
- PAGE_SIZE=-1 - Limit feature count while fetching from server. Default value is -1 - no limit.
- BATCH_SIZE=-1 - Size of feature insert and update operations cache before send to server. If batch size is -1 batch mode is disable. Default value is -1.

## Layer creation options

The following layer creation options are available:

- OVERWRITE - Whether to overwrite an existing table with the layer name to be created. The resource will delete and new one will created. This leads that resource identifier will change. Defaults to NO. Optional.
- KEY - Key value. Must be unique in whole NextGIS Web instance. Optional.
- DESCRIPTION - Resource description. Optional.

## Metadata

NextGIS Web metadata are supported in datasource, vector, PostGIS, raster layers and styles. Metadata are stored at specific domain "NGW". NextGIS Web supported metadata are strings and numbers. Metadata keys with decimal numbers will have suffix .d and for real numbers - .f. To create new metadata item, add new key=value pair in NGW domain use the SetMetadataItem function and appropriate suffix. During transferring to NextGIS Web, suffix will be omitted. You must ensure that numbers correctly transform from string to number.

Resource description and key map to appropriate description and keyname metadata items in default domain. Changing those metadata items will cause an update of resource properties.

Resource creation date maps to read-only metadata item creation_date in default domain.

Vector layer field properties (alias, identifier, label field, grid visibility) map to layer metadata the following way:

- field alias -> FIELD_{field number}_ALIAS (for example FIELD_0_ALIAS)
- identifier -> FIELD_{field number}_ID (for example FIELD_0_ID)
- label field -> FIELD_{field number}_LABEL_FIELD (for example FIELD_0_LABEL_FIELD)
- grid visibility -> FIELD_{field number}_GRID_VISIBILITY (for example FIELD_0_GRID_VISIBILITY)

## Examples

Read datasource contensts:

        ogrinfo -ro NGW:https://demo.nextgis.com/resource/1730

Read layer details:

        ogrinfo -ro -so NGW:https://demo.nextgis.com/resource/1730 Parks

Creating and populating a vector layer from a shapefile:

        ogr2ogr -f NGW "NGW:https://demo.nextgis.com/resource/1730" myshapefile.shp

### See also:

- NextGIS Web documentation
- NextGIS Web for developers