RLA (Run-Length Encoded Raster)
Mar 7,2026

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Introduction

RLA (Run-Length Encoded Raster) is a format that efficiently stores raster data using Run-Length Encoding (RLE). By recording consecutive pixel sequences with the same value as "value + repetition count," it achieves high compression efficiency, particularly for classified raster data or data with many homogeneous areas. RLA has a relatively simple data structure and has been used as a lightweight raster data storage method in image processing and GIS fields. It is suitable for raster data with high value continuity, such as elevation models, land use classifications, and binary mask data.

File Structure

The RLA format typically consists of the following elements:

Header information: Stores basic information such as the number of rows and columns in the image, cell size, data type (integer, floating-point, etc.), and compression method (RLE).
Raster data body: Stores run-length compressed data sequences for each row or in block units. Consecutive identical values are recorded in the format of "value + count."
Row offset information (implementation-dependent): May contain pointer information indicating the starting position of each row, improving random access efficiency.
Projection/coordinate information (optional): May retain coordinate systems or georeferencing information within an external metadata file or the header.

RLA is often implemented as a single file structure, characterized by its simplicity.

Pros

High compression efficiency: Extremely efficient for data with consecutive identical values, enabling significant capacity reduction in land use maps and classified images.
Simple structure: The data structure is relatively clear, making implementation and analysis easy.
Fast decompression processing: Due to the simple compression algorithm, decoding processing is fast.
Good compatibility with classification data: Suitable for storing thematic map data or mask data with few value changes.
Suitable for lightweight applications: Easy to handle as a format for small-scale data or internal processing.

Cons

Inefficient for data with low continuity: When there are few consecutive identical values, compression efficiency decreases, and in some cases, file size may increase compared to uncompressed formats.
Limited multi-band support: Not suitable for advanced multispectral data management.
Lack of advanced metadata management functions: Does not have detailed tag management capabilities like GeoTIFF.
Lack of standardization: Due to the absence of unified international standard specifications, specification differences may occur between implementations.
Unsuitable for large-scale data processing: Scalability is limited for ultra-high resolution raster data or time-series data management.

Application Scenario

RLA (Run-Length Encoded Raster) is suitable for storing classified raster data and geospatial data with many homogeneous areas, and is used in creating thematic maps such as land use maps, administrative division masks, binary images, and vegetation distribution classifications. It is also sometimes used as a lightweight internal data exchange format within image processing and GIS analysis workflows. It is particularly suitable for processing environments requiring compression efficiency and fast decompression, as well as for managing raster data with simple structures.