Dual Independent Map Encoding

Introduction

Dual Independent Map Encoding (DIME) is a data structure used in computer systems to store geographic information. It was developed by the U.S. Census Bureau in the 1960s and was widely used in geographic information systems (GIS) until the late 1990s. DIME is primarily used for encoding topological information about linear features, such as roads or rivers, and their relationships to one another.

A computer screen showing a map with lines representing roads. The lines are labeled with numbers, indicating their DIME encoding.

A computer screen showing a map with lines representing roads. The lines are labeled with numbers, indicating their DIME encoding.

Concept and Design

The DIME data structure is based on the concept of a "graph", a mathematical structure used to represent relationships between objects. In the context of DIME, the objects are geographic features, and the relationships are spatial - for example, whether one feature is adjacent to another, or whether it intersects it.

Each feature in a DIME database is represented by a "node", and each relationship is represented by an "edge". Nodes are defined by their geographic coordinates, while edges are defined by the nodes they connect. This allows DIME to represent complex spatial relationships in a simple, efficient way.

Implementation

In a DIME database, each edge is stored as a record containing the following information:

- The coordinates of the start and end nodes. - The left and right polygons (areas enclosed by edges) adjacent to the edge. - The edges adjacent to the start and end nodes. - Any additional attributes of the edge, such as its name or type.

This information allows a GIS to quickly and accurately determine the spatial relationships between features. For example, it can determine whether two features are adjacent, whether one feature intersects another, or whether one feature is enclosed by another.

Advantages and Disadvantages

One of the main advantages of DIME is its simplicity. The data structure is easy to understand and implement, and it provides a straightforward way to represent complex spatial relationships. This makes it an excellent choice for applications where speed and efficiency are important.

However, DIME also has some disadvantages. One of the main ones is that it is not well-suited to representing features that change over time. This is because each change requires updating multiple records in the database, which can be time-consuming and error-prone. Additionally, DIME does not support features with more complex shapes, such as curves or polygons with holes.

Legacy and Impact

Despite its limitations, DIME had a significant impact on the field of geographic information systems. It was one of the first data structures specifically designed for storing geographic information, and it set the standard for many of the GIS data structures that followed.

Today, DIME is largely obsolete, having been replaced by more flexible and powerful data structures. However, it remains an important part of the history of GIS, and it continues to be studied as a classic example of a topological data structure.

See Also

- Geographic Information Systems - Data Structures - Graph Theory