Sources of geodata

Geodata Standards and Exchange

The most common standards for geographical information are created and promoted by the Open Geospatial Consortium (OGC). The OGC is “an international not-for-profit organisation committed to making quality open standards for the global geospatial community”. Some of the most relevant OGC standards are the following ones:

• GML. XML-based standard to store geographical information.
• Geopackage. Portable geospatial data format that stores vector data, raster data and their associated attributes in a single SQLite database file.
• KML. XML-based format, supporting 3D visualisations and simple map annotations.
• 3D Tiles. A standard for streaming massive 3D geospatial datasets like city models or terrain to web and mobile devices.
• Sensor Things API. Standard for efficient collection, sharing, and querying of Internet of Things (IoT) sensor data, including observations and their spatial and temporal context.
• GeoSPARQL. Standard that extends the SPARQL query language to support the representation, querying, and reasoning of geospatial data on the Semantic Web.
• Filter Encoding (FE). Defines a standardised way to express spatial and non-spatial queries for use in OGC services like WFS or WMS.
• Web map services standards WMS, WMTS, WFS, WPS, CSW – see below.

Each one of these standards is described in the corresponding specification, which is subject to change and improvement. Several versions exist for each of them. Along with these standards are those made by organisations such as ISO or W3C, with a more general scope, but also important in the context of GIS. Among them, the most relevant standards are the ISO ones that define how to store metadata and the W3C standards related to communication over the Internet. Most relevant ISO metadata standards are:

• ISO 19115: Focused on describing geographic information and services, providing a framework for metadata that helps catalogue, discover, and manage geospatial data.
• ISO 19139: Defines XML schema for the implementation of metadata according to ISO 19115, making it machine-readable.
• ISO 19157: Specifies principles for evaluating and reporting the quality of geographic data, often used in metadata quality assessment.

There are also W3C standards for metadata, which are relevant in the GIS industry:

• Dublin Core (DCMI): A widely used standard for general-purpose metadata, defining 15 core elements such as "Title," "Creator," and "Date."
• RDF (Resource Description Framework): A framework for representing metadata as linked data, often used to create semantic relationships between datasets.
• SKOS (Simple Knowledge Organization System): Used for managing and linking controlled vocabularies, taxonomies, and metadata classifications.

A Shapefile is a popular geospatial vector data format created by Esri and primarily used in their software. While widely used in GIS, it is not an OGC standard. It stores geometric data (points, lines, polygons) and associated attributes in separate files.

Web Map Services

Web map services (WMS) are server-based systems that provide geospatial data and maps over the internet. These services allow users to access, view, and interact with geographic data through a web browser or GIS software without needing to download the full dataset. The data is delivered as map images (e.g., PNG, JPEG) or, in some cases, as raw vector or raster data for advanced analysis. By adhering to these standards, web map services enable seamless integration of geospatial data into diverse applications, from environmental monitoring to urban planning and disaster management.

The OGC Web Service Common (OWS) serves as a base standard for web mapping. It defines the shared protocols and behaviours that underpin WMS, WFS, WMTS, and other related services, ensuring interoperability and consistency across implementations. This standard includes:

• Request/Response Structures: Defines how clients and servers exchange data.
• Service Metadata: Ensures consistent descriptions of services (e.g. capabilities documents).
• Error Handling: Specifies standard error formats for interoperability.

Several OGC standards define individual web map services:

• WMS (Web Map Service). To serve maps as images. It defines a protocol for delivering georeferenced map images over the internet. It allows users to request maps in various formats (e.g. PNG, JPEG) and styles, based on specific parameters like geographic extent, layers, and coordinate reference systems. WMS is widely used for visualising geospatial data without transferring the underlying dataset.
• WMTS (Web Map Tile Service). To serve maps as images in preprocessed tiles. It provides fast and efficient delivery of map tiles by pre-rendering and storing fixed, tiled images at various zoom levels. It is optimised for web and mobile applications, ensuring quick map visualisation by dividing maps into manageable, pre-defined image tiles
• WFS (Web Feature Service). To serve geographical features (vector layers). It enables the retrieval of vector data over the web, allowing users to request actual geographic data in formats like GML. Unlike WMS, which serves raster map images, WFS provides access to raw data, enabling spatial analysis, querying, and manipulation of individual features. The WFS-T (Transactional Web Feature Service) extension adds capabilities for users to also update, add and delete features on the server, supporting editing and transactional workflows. This makes WFS and WFS-T ideal for applications requiring dynamic geospatial data management and real-time collaboration, such as in urban planning and field data collection.
• WPS (Web Processing Service). To serve remote processing services.It allows users to perform spatial analysis and geoprocessing tasks over the web by submitting processing requests to a server. It enables the execution of complex geospatial operations, such as buffering, reclassification or raster calculations and returns the processed results in a standard format.
• CSW (Catalogue Service for the Web). To make queries to a catalogue that contains geographical data. It enables the discovery, querying, and management of metadata about geospatial datasets and services over the web. It allows users to search for available geospatial resources based on criteria like keywords, geographic location or temporal coverage.

A popular ArcGIS Server software partially complies with OGC standards, offering support for some key services like WMS (Web Map Service), WFS (Web Feature Service), and WCS (Web Coverage Service). However, due to its proprietary nature, some ArcGIS Server services are extended beyond the OGC standards, incorporating additional features that may not be fully aligned with OGC specifications, especially for more complex workflows and data formats.

Loading geodata into GIS

In QGIS, the Data Source Manager is the ultimate place where you can connect to various types of geodata. Types of geodata supported in version 2.40 are:

• Vector data – Common file extensions include .shp, .geojson, and .gpx. Usually representing discrete features such as roads, boundaries or land parcels
• Raster data – Common file extensions include .tif, .jpg, and .png, typically used for continuous data such as satellite imagery, elevation models or land cover classification.
• Mesh – Represents 3D surfaces using interconnected nodes (vertices) and edges, forming a network of triangles or polygons to model complex geometries like terrain or buildings. It is typically used for high-resolution modelling of surfaces and is associated with file extensions such as .ply, .tin, or .adf.
• Point Cloud – Point cloud data consists of a large collection of individual points in 3D space, often captured by laser scanners (LiDAR) or photogrammetry, representing surfaces and objects in high detail. Common file extensions include .las (LASer file format), .laz (compressed LAS), and .xyz (XYZ text format), typically used in applications like topography, infrastructure modelling, and environmental monitoring.
• Delimited Text – Delimited text data stores spatial information in plain text format, with coordinates and attributes separated by a specific delimiter (e.g. commas, tabs). Common file extensions include .csv (Comma-Separated Values), .txt (Text), and .tsv (Tab-Separated Values).
• Geopackage – Open, standards-based and container format for storing both vector and raster data in a single SQLite database file. The file extension is .gpkg.
• GPS – GPS data refers to coordinates collected from GPS devices, representing locations on Earth in latitude, longitude and sometimes elevation. The common file extension for GPS data is .gpx (GPS Exchange Format). This format is used to store waypoints, tracks and routes, commonly for navigation, outdoor activities and mapping purposes.
• SpatiaLite – SpatiaLite is an extension to SQLite that enables the storage and management of spatial data within a lightweight, file-based database. The file extension is .sqlite or .db, and it supports both vector and raster data, along with spatial indexing and geospatial queries.
• PostgreSQL – PostgreSQL is an open-source relational database management system that, with the PostGIS extension, supports the storage and querying of spatial data. It is used to store large-scale vector and raster datasets with advanced spatial indexing and geospatial operations. The format does not have a specific file extension, as it is a server-based system.
• MS SQL Server – MS SQL Server is a relational database management system that, with the Spatial Data extension, supports the storage and querying of spatial data. The format does not have a specific file extension, as it is a server-based system.
• Oracle – Oracle Spatial is an extension of the Oracle Database that enables the storage, management, and analysis of spatial data. It supports both vector and raster data, offering powerful spatial indexing, geospatial functions, and advanced querying capabilities. As a server-based system, it does not have a specific file extension.
• Virtual Layer – A Virtual Layer in GIS is a layer that represents data derived from a query or a combination of multiple data sources, without physically storing the data itself. It is typically used to perform complex queries or operations on data from various formats, like Shapefiles, PostGIS, or SpatiaLite, without the need to import or replicate the data. Virtual layers in QGIS are defined using SQL queries, and they do not have a specific file extension since they are dynamically generated based on the query results.
• SAP HANA – SAP HANA is an in-memory, column-oriented relational database management system that supports spatial data through its SAP HANA Spatial extension. It allows for the storage and analysis of both vector and raster data, offering advanced spatial indexing and geospatial queries. As a server-based system, it does not have a specific file extension.
• WMS/WMTS – WMS delivers maps as static images (typically in formats like PNG or JPEG) generated from spatial data, while WMTS serves maps as tiled images that allow for more efficient navigation and zooming. These services do not store spatial data directly but provide access to it via web requests. Both formats rely on standard web protocols (HTTP, XML) for data delivery.
• WFS / OGC API - Features – Serving vector data over the web, allowing users to request, query, and interact with geospatial features. WFS provides access to raw geographic features in formats like GML or GeoJSON, while the newer OGC API - Features offers more modern RESTful access to spatial data, with JSON or GeoJSON as common output formats. Both standards allow for spatial queries and can support editing or updating features in some configurations.
• WCS – WCS is a standard for serving raster data over the web, allowing users to request grid-based data (such as satellite imagery, elevation models, or temperature maps) in formats like GeoTIFF or NetCDF. Unlike WMS, which provides static image maps, WCS delivers the actual data (as raw pixels or values), enabling users to perform further analysis or processing on the raster data. It supports spatial queries and can return data in different coordinate reference systems.
• XYZ – The XYZ format refers to a simple tile-based system for serving map data, commonly used for web mapping services. In this format, map data is divided into square tiles (typically 256x256 pixels) at various zoom levels, and the tiles are indexed using a coordinate system based on X (longitude), Y (latitude), and Z (zoom level). XYZ tiles are often used in web mapping platforms like OpenStreetMap or Google Maps, where tiles are dynamically requested from a server as the user zooms or pans the map.
• Vector Tile – Vector tiles are a format for serving map data as vector graphics, rather than raster images, which allows for more flexibility and interactivity in web maps. The map data is divided into tiles at various zoom levels, but instead of pixels, the tiles contain geometries (points, lines, polygons) and attributes, usually in formats like PBF (Protocol Buffers). Vector tiles enable client-side rendering, making maps more responsive and customizable, and are commonly used in applications like Mapbox or in services that require high-performance mapping.
• Scene – A scene refers to a 3D representation of a geographic area, typically used for visualising spatial data in a three-dimensional environment. Scenes combine various types of data, such as terrain, buildings and other features, to provide a realistic view of a landscape or urban area. In modern applications, scenes are often supported as Cesium 3D Tiles files (such as tileset.json) or through server connections to Cesium 3D Tiles or Quantized Mesh, allowing for the efficient streaming and visualisation of large-scale 3D data.
• ArcGIS REST Server – An ArcGIS REST Server is a web service provided by Esri's ArcGIS Server that allows users to access and interact with GIS resources via RESTful APIs. It supports both vector and raster data, enabling functionalities like querying, editing and analysing geographic information through web requests. The service can expose layers, maps, geoprocessing tools and spatial analysis functions, making it ideal for integrating GIS capabilities into web applications.
• Sensor Things – Provides a RESTful interface to interact with data from IoT (Internet of Things) sensors, including environmental data like temperature, humidity, and air quality, and spatial information such as location and time. The API allows for querying and managing sensor data, with responses typically in JSON format, enabling seamless integration of sensor data into GIS applications and real-time monitoring systems.

In QGIS, the process of connection to a WMS/WMTS, WFS or WCS server is similar. First, you must specify a connection to the server. If you have not yet specified any connection before, click “New”.

Data Source Manager for WMS/WMTS connection.

In the dialog window for a new connection, you always must specify at least its name (what it will be called in the list of connections) and a URL of the WMS, WMTS, WFS, WCS server. Getting a correct URL of the server is crucial. It usually looks somewhat like https://ags.cuzk.cz/arcgis1/services/ORTOFOTO/MapServer/WMSServer – the last part containing the words wms, wmsserver, wfs, ows or alike. The other options in the dialog window control possible authentication methods, WMS server version and other advanced parameters.

Correctly specified connection to a WMS server in QGIS.

Once the connection to the WMS / WMTS / WFS / WCS server is created, it remains available in the drop-down list and you do not need to specify it again every time you want to connect to the same server. You can even save the list of connections you have specified to a file and transfer it to another machine or another installation of QGIS. The “Save”/”Load” buttons serve this purpose.

Click “Connect” to connect to the selected WMS / WMTS / WFS / WCS server. A list of layers shall appear in the area in the middle of the window. From the layers in the list, select the one that is of your interest. You can usually change the file format in which the map or features will be loaded into the map canvas and the spatial reference system of the map / features. Once all is selected best for your needs, click “Add”.

The connected WMS server provides only one layer called “ORTOFOTO”. File format JPEG and spatial reference system WGS 84 were selected for the layer.

The selected layer is added on top in the “Layers” panel. You may want to reorder the layers with drag and drop to see the map content in the correct order.

Layer “ORTOFOTO”, which is an aerial imagery, successfully loaded into QGIS.

In HSLayers-based WebGIS applications you can add data via the “Datasources” panel, which can be opened by the “Add external data” menu entry.

An HSLayers-based WebGIS application with expanded menu and “Add external data” highlighted.

It is possible to add data from three places:

• The data catalogue connected with the WebGIS application.
• A file, database or a web service on the internet identifiable with an URL.
• A file in the user’s local filesystem.

Adding data from the map catalogue is as simple as clicking the name of the interesting layer and then the “Add to map” button. As an asset, the geographical extent of the layer is highlighted in the map canvas.

Adding a layer “LPIS Horice” into the HSLayers-based WebGIS map.

Connecting to a WMS / WMTS / WFS layer from an HSLayers-based WebGIS application is somewhat similar to the approach in QGIS. You first have to input the URL of the remote server to which you want to connect. Then click the chainlink connection button, which loads the list of available layers and available options. After ticking the desired layer in the layer list, click “Add to map” and the layer will appear in the map canvas.

The provided WMS server only offers one layer “ORTOFOTO”, which is being added to the map.

You may want to reorder the map layers in the Layer Manager panel as the latest added layers are usually displayed on top.

An HSLayers-based WebGIS application with two layers. One from a WMS server and the other from a connected data catalogue.

Third option is to add a local file. This can be done by selecting the appropriate file in your device’s file system. First you must select which format of data you wish to add (KML, GPX, GeoJSON, etc.), then you choose the file(s) from your device. Once the file(s) are read, the UI displays how many features will be added (in case of vector data). You have an option to rename the layer or to add a style file (in SLD or QML format) which will control the layer’s appearance. If you won’t provide a style file, the application will set a default style for all the data. Once done, click the “Add to map” button.

Adding a GeoJSON file with 596 features into the HSLayers-based WebGIS application.

The local layer “zones” over the WMS layer “Prohlížecí služba pro ortofoto ČR”.