QLR (QGIS Layer Definition File)

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Introduction

QLR (QGIS Layer Definition File) is a layer definition file used by QGIS (an open source GIS software). QLR files do not store the data source itself, but rather the configuration information of the layer, such as style, symbols, labels, etc.

File Structure

QLR files are in XML (Extensible Markup Language) format and contain the following information:

Data source information (SHP, GeoJSON, PostGIS, WFS, etc.)
Style settings (color, line thickness, labels, transparency, etc.)
Symbol settings (points, lines, polygons, etc.)
Filter conditions (display rules based on specific attribute values)
Coordinate Reference System (CRS) information

Because of the XML format, QLR files can easily manage and share reusable layer settings in QGIS.

Pros

1. Centralized management of layer settings: QLR files can be used to unify layer styles and property settings within QGIS, simplifying management.

2. XML format, easy to read and edit: QLR files can be modified directly using a text editor, making it easy to adjust manually or use as a template.

**3. Apply settings without modifying the data source: **QLR only stores references and style settings of the data source, without affecting the original data.

4. More convenient team collaboration: Multiple users can use the same QLR file to maintain unified layer settings and improve consistency.

Cons

1. Does not contain the data itself: QLR files only store the path and style of the data source, and the data (such as SHP, GeoJSON) needs to be managed separately.

2. Only applicable to QGIS: QLR is a proprietary format of QGIS and cannot be used directly in other GIS software such as ArcGIS.

3. Changes in data path will lead to inaccessibility: QLR relies on the storage path of the data. If the data location changes (such as changes in the path of the network drive or remote server), QLR may not be able to load the data correctly.

Application Scenario

When multiple GIS users or teams need to use unified layer settings, QLR files can be used for centralized layer management. If you need to use the same layer settings in different projects, you can use QLR files to maintain consistency and reuse layers. QLR files can share layer settings between different QGIS projects without changing the data storage location or properties. For example, database connection information such as PostGIS or WFS can be saved in a QLR file, so that multiple projects can apply the same database layer configuration, thereby ensuring consistency in data visualization and analysis.