Summary for Spatial Data

In today’s data-driven world, where everything is interconnected, and location plays a crucial role, spatial data has become increasingly important. Spatial data refers to information associated with specific geographic locations, enabling us to analyze, visualize, and understand the world around us. Relational database management systems like MySQL offer powerful features for storing and processing spatial data. With different types of spatial entities, functions, and operators, MySQL provides rich capabilities for us to explore.

Spatial data types and formats

The OpenGIS model defines a hierarchy of geometries, including Point, Curve, Surface, and GeometryCollection, with Geometry being the root. GeometryCollection allows for combining different spatial types, such as MultiPoint, MultiCurve/MultiLineString, and MultiSurface/MultiPolygon, with only the latter instantiable variants usable. MySQL adapts the OpenGIS model by providing corresponding data types. The GEOMETRY data type can store any spatial type, while POINT, LINESTRING, and POLYGON specialize in their respective shapes. Moreover, MULTIPOINT, MULTILINESTRING, and MULTIPOLYGON can hold collections of their single-value counterparts, and GEOMETRYCOLLECTION can store a mix of any spatial data types. As storing spatial entities in plain text could result in substantial storage overhead, MySQL offers three distinct data formats for storing spatial entities: Well-Known Text (WKT), Well-Known Binary (WKB), and internal geometry storage.

Creating spatial entities

MySQL offers a range of functions for creating different types of spatial geometries. For instance, to create POINT geometries from string input, there’s the ST_PointFromText() function or the Point() function for direct point creation. Similarly, LINESTRING geometries can be generated using the ST_LineStringFromText() or the LineString() function. These allow for inputting coordinates to delineate paths. MySQL provides the ST_PolyFromText() function or the Polygon() function for creating polygons. Beyond these, MySQL provides functions for spatial entity collections, such as MultiPoint() and MultiPolygon(), which aggregate multiple Point() and Polygon() entities, respectively. These collection functions follow a consistent underlying principle that applies to all functions that allow for creating collections. Note that the MySQL-specific functions for creating spatial entities, e.g., Point(), refer to the spatial reference system (SRS) with ID 0, unlike their counterparts, which enable specifying the desired SRS.

Spatial operators

ST_Intersection() is employed to compute the intersecting area between two geometries, creating a new geometry encapsulating this shared space. In contrast, ST_SymDifference() highlights two geometries’ distinct, non-overlapping segments. We use ST_Union() for merging geometries, proving particularly effective in scenarios like optimizing parking zone layouts by combining intersecting zones. ST_ConvexHull() takes a different approach, calculating the smallest convex shape that fully encloses a given geometry, aiding in strategic planning like optimal e-scooter parking placement. Lastly, ST_Transform() transforms a geometry to a different spatial reference system, not just changing its associated SRS like ST_SRID() but also adjusting its coordinates to align with the new SRS, thus actively modifying its properties.

Analyzing properties of and relationships between spatial entities

Analyzing spatial entities such as points, lines, and polygons is accomplished through distinct functions. Points, essentially characterized by their coordinates, are analyzed using ST_Longitude() and ST_Latitude() for geographic SRS and ST_X() and ST_Y() for both geographic and cartesian SRS to determine their precise longitude, latitude, and coordinates. For lines, such as tracking routes in applications like e-scooter services, functions like ST_StartPoint() and ST_EndPoint() are utilized to identify the beginning and ending points of LINESTRING geometries. In the case of polygons, the function ST_Area() calculates the area of POLYGON or MULTIPOLYGON geometries, with the output varying based on the embedded SRS. The function measures the area in square meters for geographic SRS and cartesian terms for cartesian SRS.

Analyzing relationships between spatial entities involves a variety of functions tailored to specific needs. Distance measurement is a key aspect for which MySQL offers functions like ST_Distance() to compute the Euclidean distance between two entities, ST_FrechetDistance() to measure the similarity between curves, and ST_HausdorffDistance() to find the greatest distance between two geometries. These functions help in applications such as guiding customers to the nearest e-scooter by calculating the shortest distance. Containment detection is another crucial functionality, addressed by the ST_Contains() function, which checks whether one spatial entity completely encloses another, essential for ensuring e-scooters are parked in designated zones. Additionally, MySQL provides functions that use the minimum-bounding rectangle of geometry rather than its precise shape, which is beneficial for handling large datasets and reducing the computational load in initial filtering steps before applying more complex spatial functions.

Working with documents in GeoJSON

GeoJSON, a geospatial data interchange format based on JSON, encodes various geographic data structures like Point, LineString, Polygon, and their collection counterparts, along with Feature and FeatureCollection objects. In MySQL, the transformation of GeoJSON to spatial entities is handled by the ST_GeomFromGeoJSON() function, which requires a string representing the GeoJSON document, an optional parameter for multidimensional coordinates, and the SRS ID. Conversely, the ST_AsGeoJSON() function allows for the reverse process, converting spatial entities back into GeoJSON format. This function takes parameters specifying the geometries for conversion, the precision of coordinates, and a bit mask for adding a bounding box and coordinates reference system (crs) to the GeoJSON document.