SDTS (Spatial Data Transfer Standard)
May 25,2026

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Introduction

SDTS (Spatial Data Transfer Standard) is a spatial data exchange standard developed in the United States, designed to enable lossless conversion of geographically referenced data between different computer systems. By defining a unified three‑layer model (conceptual, logical, and format), it ensures the integrity of vector and raster data during transmission and supports the simultaneous exchange of metadata. The standard was confirmed as a U.S. Federal Information Processing Standard (FIPS 173) in July 1992. Led by the U.S. Geological Survey (USGS), SDTS has been widely used for spatial data sharing among federal agencies, local governments, and commercial organizations.

File Structure

The file structure of SDTS is based on a layered, modular model designed to support complete and lossless exchange of spatial data. Its core structure can be divided into the following key components:

Logical Specifications layer: The foundation of SDTS, defining a common logical model for data exchange. It consists of records, fields, and subfields, and includes a total of 34 standard module types used to organize global information, data quality, spatial objects, attribute data, coordinate reference, and various other content.
Data Quality Module: Provides a description of data reliability, covering five aspects: source, positional accuracy, attribute accuracy, logical consistency, and completeness, helping users assess the suitability of the data.
Spatial Object Modules: Used to represent digital forms of geographic entities, supporting various geometry types such as points, lines, polygons, and rasters. For example, actual files may contain layers such as LE01 (line string) or PC01 (polygon).
Attribute Modules: Store non‑spatial attribute information associated with spatial objects, such as road names and administrative division codes, ensuring that semantic information is not lost during conversion.
Graphic Representation Modules: Contain cartographic symbol information, such as text labels, line styles, fill patterns, and color indices, used to maintain visual consistency between different systems.
Lineage and Directory Modules: Record the data’s source, processing history, and transmission path, and organize the internal modules of the file through a directory structure, facilitating quick location and parsing.
Physical Format Layer: Actual data is stored in binary or text files conforming to the ISO 8211 standard. File extensions are typically .ddf. Data may be organized by region (e.g., state level), such as the Maryland transportation data file MDTRCATD.DDF.

Pros

Data integrity and cross‑platform compatibility: By defining a strict logical model and physical format (based on ISO 8211), SDTS ensures that vector and raster data are transmitted between different systems without loss of information. It supports complex spatial structures (e.g., topological relationships) and simultaneous exchange of metadata, improving the reliability of data sharing.
Strong standardization and generality: As a FIPS 173 federal standard, SDTS has been widely used by government agencies, research institutions, and the private sector, providing a unified data conversion mechanism and promoting integration and interoperability of multi‑source geographic data.
Flexible and extensible modular design: Its layered architecture (e.g., topological vector module, raster module, transportation network module) allows the development of “profiles” for specific data types, enabling efficient and accurate data exchange within particular domains.

Cons

High technical complexity and implementation cost: The SDTS specification is large and complex to implement, resulting in a high barrier to software development and data conversion. Ordinary users find it difficult to work with directly, requiring specialized tools and training, which limits its adoption.
Superseded by more modern standards: Since 2014, the U.S. Federal Geographic Data Committee (FGDC) has officially recommended replacing SDTS with GML (Geography Markup Language) , as GML is better suited to the web environment and XML ecosystem. SDTS has gradually fallen out of mainstream use.
Outdated file format and difficult to read: The actual .ddf files are based on the ISO 8211 binary format, which lacks human readability. Support in modern GIS software is limited, often requiring dedicated conversion tools for import, affecting usability.

Application Scenario

SDTS is primarily used in government agencies, the geographic information system (GIS) industry, and research fields. As a Federal Information Processing Standard (FIPS 173), it has been widely employed for spatial data sharing and archiving among federal, state, and local government departments in the United States. The standard supports lossless exchange of various types of geographic information, including topographic maps, transportation networks, hydrographic data, and geological surveys. It has played a central role in the construction of the National Spatial Data Infrastructure (NSDI) , ensuring the integrity and consistency of vector and raster data transmission across different systems.