TopoJSON
An extension of GeoJSON that encodes topology.
TopoJSON is an extension of GeoJSON data format, founded on the premise of encoding geospatial data structures topologically. Unlike other forms of GIS data formats, TopoJSON employs arcs, which are sequences of points rather than properties attached to each point, vastly simplifying the representation of contiguous or nested features.
The format, TopoJSON, was specifically designed for topological geospatial operations. In topology, boundaries and features are not denoted as separate, conflicting entities but relative sequences of points called “arcs”. These arcs build the topological superstructure providing efficiency and a robust database. TopoJSON files can contain points, lines, polygons, and multi-part collections of these types. By leveraging arcs, TopoJSON dramatically reduces redundancy and typically results in smaller file sizes.
The primary strength of TopoJSON comes from the 'topology' aspect it imbibes. Topology, a critical branch of mathematics, deals with properties of space that are preserved under continuous transformations, such as stretching and bending, and has widespread utilities in GIS.
By expressing multiple geometries in terms of shared sequences of geographic locations (arcs), TopoJSON facilitates more efficient streaming, visualization, and real-time processing of geospatial data specifically in the browser environment. This implementation reduces the redundancy in the data sets, facilitating a noticeable decrease in file size as compared to standard GeoJSON.
Geometries in TopoJSON are expressed explicitly with arcs. These arcs are sequences of points, while line strings and polygons are defined as a list of these arc sequences. This means that the shared borders in complex polygons are only recorded once, massively reducing the file size and aiding in faster processing and loading times.
The TopoJSON specification also supports the incorporation of additional map features, such as simplification and quantization. Simplification reduces the number of points in a shape for quicker drawing and lowers memory usage, while quantization transforms floating point numbers to a relative integer grid, thus reducing file size. These supplementary features clearly highlight the adaptive and professionally oriented nature of the TopoJSON data format.
However, it is noteworthy that the more complex nature of TopoJSON compared to GeoJSON may lead to increased processing times and complexities. The decoding of TopoJSON would require extra processing to convert the arc sequences back into traditional GIS geometries.
In conclusion, TopoJSON enables compact encoding of topological structures in a manner optimized for the modern web. It has core strengths in its provision for reduction in file size and the support for manifold GIS operations, alongside some inherent complexities and processing load. As GIS data evolves, so are data formats like TopoJSON, showcasing the synergistic relationship between data representation and geographical information systems.
