Introduction

A dataset is a collection of records, where each record has a defined number of elements and the data type of each element is defined. The elements are commonly referred to as attributes. For example, the dataset of street names shown in Table 2 consists of records that have the attribute headings of “Name” and “Street Type” with the data types letters and spaces and letters respectively. In this example, Street Type contains values from the set {‘Lane’, ‘Road’, ‘Street’, ‘’}. The first three values ‘Lane’, ‘Road’ and ‘Street’ are obvious – but what about the last value of ‘’? ‘’ is a deliberate empty set of character values! In our world there are many streets that have no type, and, indeed there are many that have no name. Here, the use of an empty set of characters, or ‘’, indicates that the Street Type attribute has no type, not that the type is unknown (null).

Table 2 An example of a road name dataset.

Name (letters and spaces)	Street Type (letters)
Picton	Road
Menangle	Street
The Boulevard	[1]

Geospatial datasets contain one or more values that refer to a location on earth. For the majority of geospatial datasets, the location consists of one or more points, lines, and/or polygons, that are referenced to a coordinate system that is a projection of the earth’s surface.

For this project, any dataset element type that stores the geospatial shape with respect to a referenced coordinate system is called a geometry. Any empty geometry element is a geometry that doesn’t have any of the vertices which are required to construct a shape.

In many organizations geospatial datasets are contained within enterprise databases where frequently the same brand of enterprise database is used elsewhere within the same organization to contain non-spatial datasets. For example, a local government office may use one or more MicroSoft SQL Server installations as a dataset repository for: a content management system; a customer relationship management system; a land management system; an asset management system; and, a Geographic Information System (GIS).

QGIS [3] is a computer program that among other things is used to view, create and edit the geometry values within geospatial datasets. For many data sources QGIS does not: Parse null and empty geometry values equivalently for different data storage formats; does not directly show which records within a dataset have null or empty geometry elements; and, does not always process null and empty geometry elements as specified by international or open geospatial standards.

A conceptual description of datasets, geometry data types, and, null and empty data values are outlined in the Background section.

[1]	The street name Boulevard is also a type of street, consequently the Street Type field is empty.