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1 Introduction

This Spatial Data Transfer Standard (SDTS) provides a solution to the problem of spatial (i.e., geographic and cartographic) data transfer from the conceptual level to the details of physical file encoding. Transfer of spatial data involves modeling spatial data concepts, data structures, and logical and physical file structures. To be useful, the data to be transferred must also be meaningful in terms of data content and data quality. SDTS addresses all of these aspects for both vector and raster data structures.

The base standard is in three parts. Part 1 addresses the logical specifications in terms of conformance requirements, a conceptual model, quality specifications, the data structure model, and the transfer format. Part 2 addresses data content by providing a standard list and definitions of spatial features and their attributes. Part 3 specifies the implementation of SDTS in terms of the International Organization for Standardization for a Data Descriptive File for Information Interchange. Subsequent part numbers are assigned to profiles. A SDTS Profile is a normative part of this standard and is a subset of this standard but may also include extensions to this standard. A SDTS Profile is defined for use with a specific data model, application domain, or other such purpose.

Section 1 of part 1 includes a statement of scope (1.1, Scope of SDTS) and conformance requirements (1.3, Conformance) for SDTS. It also includes normative references to other standards (1.4, References) and definitions of terms (1.5, Definitions).

The conceptual model of spatial data (2.1, Conceptual Model) is presented in section 2 to provide a framework for defining spatial features (2.1.3, Model of Spatial Features) and a context for the definition of a set of spatial objects (2.1.2, Model of Spatial Objects). This conceptual model supports the translation of user data models to and from the SDTS model. Within section 2 is a defined set of spatial objects, for zero, one, and two dimensions, used in spatial data systems to represent real-world spatial phenomena. Three or higher dimensional spatial objects have not been specified for vector objects, but definitions have been provided for multi-dimensional raster objects (2.3, Definition of Spatial Objects). The defined set of spatial objects will support the three major types of spatial data operations: geometry only, geometry and topology, and topology only. (2.2, Classification and Intended Use of Objects) These objects have been specified in a modular fashion so that more elaborate composite objects can be constructed from them.

Section 3, Spatial Data Quality, includes specifications for a quality report concerning the objects in a transfer and their attributes. The purpose of the quality report is to provide detailed information for a user to evaluate the fitness for a particular use. This style of standard can be characterized as "truth in labeling," rather than fixing arbitrary numerical thresholds of quality. To implement this portion of the standard, a producer is urged to include the most rigorous and quantitative information available on the components of data quality described in this section.

Sections 4, General Specification, and 5, Transfer Module Specification, present specifications for the transfer of spatial data. Section 4 contains general concepts and specifications (4.1, Spatial Data Transfer Models) of the underlying models that pertain to the transfer module specifications of section 5. Section 4 also specifies the general elements of an implementation, the relationships of the logical constructs of the data models to the general elements of a detailed implementation, and general constraints on the implementation (4.1.3, The Transfer Model.) Finally, section 4 presents the transfer module specification conventions used in section 5 (4.2, Transfer Module Specification Conventions). Logical modules consisting of detailed record, field and subfield specifications are presented in section 5, Transfer Module Specification.