Sustainability of Digital Formats: Planning for Library of Congress Collections

ArcGIS Layer Files are proprietary GIS metadata storage files used in Esri products. These files store all settings for Layer file properties. According to Esri, this includes anything that a Layer file can store, including symbology, symbology classifications, labeling properties, scale ranges, feature templates, and definitions. This includes color shading, naming, and label properties. According to Esri, Layer files do not contain geographic data, but rather act as a pointer to a dataset's physical location. Layer Files ensure the same symbology will be displayed on another map. As outlined in the ArcGIS documentation, there are numerous types of layers, and not all of them support the same set of properties.

ArcGIS Layer Files are directly readable only by ArcGIS software. ArcGIS Pro offers a Python SDK, arcpy.mp, which can access information about the layers. The ArcGIS documentation outlines, in detail, what Layer files can store. To use an ArcGIS Layer File, the user must also have an associated data file with the same prefix name saved in the same part of the filesystem.

ArcGIS Layer Files are defined as having LYRX or LYR as a file extension. While LYR and LYRX files are intended for the same purpose, they are technically distinct from each other. LYRX files are in a JSON-based text format and LYR files are an OLE2-based binary format. ArcGIS Pro can read legacy LYR files but can only save as LYRX files.

LYRX files are the extension used in Esri's ArcGIS Pro. LYRX files can store multiple layers and/or multiple group layers at the root level.

LYR files are the extension used in Esri's ArcGIS versions 10.X and ArcGIS Desktop. LYR files can only store a single layer or a single group layer at the root level. A group layer can have multiple layers or group layers within it.

ArcGIS Layer Files are often found alongside EsriShapefiles. According to North Carolina State University, the Shapefile is considered an industry standard geospatial data format, and widely compatible with other GIS software. Shapefiles comprise of at least three files that must all be saved in the same workspace.

In ArcMap, Layer files are created by right-clicking a feature class. In ArcGIS Pro, creating Layer Files depends on if the user is creating individual or group Layer Files. Layers can be referenced from within a project using the listLayers method in the Map or LayerFile class. More information about a layer can be retrieved by inspecting the Describe Object returned by the layer property.

Limited documentation around the file format itself, with some documentation featuring how to use the format within the context of the applications.

Esri publishes a Cartographic Information Model specification on GitHub including the CIMLayerDocument definition used for saving LYRX files.