Geospatial measurement sublevels
The Geospatial measurement level, which is used with the List storage type, has six sublevels that are used to identify different types of geospatial data.
- Point. Identifies a specific location (for example, the center of a city).
- Polygon. A series of points that identifies the single boundary of a region and its location (for example, a county).
- LineString. Also referred to as a Polyline or just a Line, a LineString is a series of points that identifies the route of a line. For example, a LineString might be a fixed item, such as a road, river, or railway; or the track of something that moves, such as an aircraft's flight path or a ship's voyage.
- MultiPoint. Used when each row in your data contains multiple points per region. For example, if each row represents a city street, the multiple points for each street can be used to identify every street lamp.
- MultiPolygon. Used when each row in your data contains several polygons. For example, if each row represents the outline of a country, the US can be recorded as several polygons to identify the different areas such as the mainland, Alaska, and Hawaii.
- MultiLineString. Used when each row in your data contains several lines. Because lines cannot branch, you can use a MultiLineString to identify a group of lines (for example, data such as the navigable waterways or the railway network in each country).
Be aware of these restrictions when using geospatial data:
- The coordinate system can affect the format of the data. For example, a Projected coordinate system uses the coordinate values x, y, and (when required) z, whereas a Geographic coordinate system uses the coordinate values longitude, latitude, and (when required) a value for either altitude or depth.
- A LineString can't cross over itself
- A Polygon is not self-closing; for each Polygon you must ensure that the first and last points are defined as the same.
- The direction of the data in a MultiPolygon is important; clockwise indicates a solid form and counterclockwise indicates a hole. For example, if you record an area of a country that contains lakes, the main land area border can be recorded in a clockwise direction and the shape of each lake in a counterclockwise direction.
- A Polygon can't intersect with itself. An example of this intersection would be if you tried to plot the boundary of the polygon as a continuous line in the form of a figure 8.
- MultiPolygons can't overlap each other
- For Geospatial fields, the only relevant storage types are Real and Integer (the default setting is Real)