Data Management

Database management system (DBMS) uses the data models specifications in establishing consistency in the data management. To this end a data model must have three basic components,

1. Data feature types to form a data structure that describe the data,

2. Rules that establish the accuracy and maintain the structures and/or operations for validating data

3. Data operators that process data structures that allow data manipulation.

A spatial database is a type of database that is designed to store and manage spatial data, which represents objects defined in a geometric space.

Data Model

A data model is a way of demonstrating the framework or structure and relationships of data in a database. Utilised to represent, organize, and manage data in a systematic and consistent manner. Spatial data models are a critical component of geographic information systems (GIS) and are designed to facilitate the storage, retrieval, analysis, and visualization of geographic information. There are several types of spatial data models, each with its own approach to representing spatial data.

Database Structure

The Queensland Government stores its topographic data as feature classes of similar data themes within a spatial Postgres database. This ESRI cloud-based database is the point of truth for topographic data and stores the data in geographic coordinates (latitude and longitude) on the Geocentric Datum of Australian 2020 (GDA2020). Each dataset within the database is accompanied by metadata that describes the dataset, licensing, and attribution to ISO19115/ISO19139 standard. Additionally, an editable database is available within this environment that allows for the management, maintenance, and creation of features.

Reference System

Reference system, also known as a spatial reference system, is a framework for specifying and locating geographic phenomena in a standardized and consistent manner. These systems define a set of rules and parameters that enable the accurate positioning and referencing of objects or locations on the Earth's surface. They are essential for spatial data integration, analysis, and mapping. There are several key components within a spatial data reference system:

·         Coordinate System: The coordinate system specifies how geographic positions are represented in terms of coordinates, which are typically expressed in latitude and longitude or easting and northing values. Common coordinate systems include geographic (e.g., WGS84) and projected systems (e.g., UTM or State Plane), each with specific units of measurement.

·         Datum: A datum defines the origin, orientation, and scale of the coordinate system. It provides a reference point, typically located on the Earth's surface, from which all other geographic positions are measured. Different datums can result in variations in positional accuracy, so it's important to use the correct datum for a specific area or dataset.

·         Projection: In cartography, a map projection is a set of transformations (mathematical calculations) that convert the angular geodetic coordinates of the geographic coordinate system to Cartesian coordinates of the planar projected coordinate system. The numbers of the coordinate system provide a frame of reference to locate features on the Earth's surface, to align data relative to other data, to perform spatially accurate analysis, to add to and edit the data, and to create cartographic products. Different map projection methods are suited for different applications some commonly used projections include the Mercator, Lambert Conformal Conic, and Albers Equal Area.

·         Units of Measurement: Spatial reference systems define units of measurement for coordinates, such as degrees, meters, or feet, depending on whether they are geographic or projected coordinate systems.

·         Ellipsoid: In geographic coordinate systems, the Earth's surface is approximated as an ellipsoid. The ellipsoid model used in a reference system defines the shape of the Earth and impacts calculations involving distances, areas, and angles.

·         Grids and Graticules: Grids and graticules provide a set of lines or a network of intersecting lines on maps to aid in locating and measuring features. For instance, a graticule consists of lines of latitude and longitude on a map.

·         Zone Designations: Some reference systems divide the Earth into zones to improve accuracy. For example, the Universal Transverse Mercator (UTM) system divides the Earth into multiple zones, each with its own unique coordinate system to minimize distortions.

·         Registry and Authorities: Many reference systems are standardized and maintained by geospatial authorities. These organizations define and publish reference system specifications to ensure consistency and interoperability among GIS and mapping applications.

Spatial data reference systems are essential for geographic data interoperability and the accurate integration of data from various sources. Users need to be aware of the reference system used in their spatial data and ensure consistency when working with different datasets, as using incompatible reference systems can lead to spatial data misalignment and errors.

The Queensland Government Digital Topographic Data is currently represented as vector features in geographic coordinates (Latitude/Longitude) using Geocentric Datum of Australia 2020 (GDA2020) reference system with elevations (where stored) on Australian Height Datum (AHD71).

Data Types

Data types represented in Queensland Government’s Topographic Data set, comprises of vector data models containing objects in point, line, and polygon format.  Attributes are associated with these geometric objects to provide additional information.  The vector data model is suitable for representing discrete, well-defined features and is often used for mapping, cartography, and spatial analysis.

Metadata

ISO 19115 is an international standard for geospatial metadata, and it provides a comprehensive framework for describing geospatial datasets and related resources. Metadata based on ISO 19115 includes information about the dataset's content, quality, spatial and temporal characteristics, and more. To create metadata compliant with ISO 19115, a set of specific information must be provided. A high-level overview of the elements typically included in ISO 19115 metadata that may or may not be represented within the Topographic data are -

Identification Information:

·         Title: The title or name of the dataset.

·         Abstract: A summary of the dataset's content and purpose.

·         Date: The date the metadata was created or last updated.

·         Citation: The formal reference for the dataset.

·         Citation Contacts: Contact information for the person or organization responsible for the data.

·         Data Quality Information:

·         Lineage: Describes the dataset's history, including how it was created, processed, and updated.

·         Completeness: Information on the completeness of the dataset.

·         Positional Accuracy: Information about the accuracy of the geographic positioning of features.

·         Attribute Accuracy: Information about the accuracy of the data attributes.

·         Logical Consistency: Details on logical consistency checks applied to the data.

Spatial Representation Information:

·         Geometric Object Types: Describes the types of geographic features (e.g., point, line, polygon).

·         Spatial Reference System: Information about the coordinate reference system used in the dataset.

·         Topology Information: Information about topological relationships between features.

·         Spatial Data Organization: Information about the structure of the dataset, including data formats, scales, and any aggregation or distribution of data.

Reference System Information:

·         Information about the coordinate reference system, including the datum, projection, and units of measurement.

·         Metadata Reference Information: Metadata standard used: Specify that ISO 19115 is the standard.

·         Metadata Profile: Indicate if any specific profiles or extensions of ISO 19115 are used.

·         Distribution Information: How the dataset can be accessed and distributed, including online links, file formats, and access restrictions.

Metadata Constraints:

·         Any constraints or restrictions on the use of the metadata, such as copyright or licensing information.

·         Metadata Contact: Contact information for the person or organization responsible for the metadata.

·         Data Character Set: Specifies the character encoding used in the metadata.

·         Spatial Data Themes: Keywords and controlled vocabulary terms that describe the dataset's subject matter.

·         Temporal Extent: Information about the time period covered by the dataset.

Maintenance Information:

·         How often the dataset is updated and information about data maintenance.

·         Use Limitations: Any limitations or constraints on the use of the dataset.

·         Additional Information: Any other relevant information about the dataset.

Figure 1 – Extract of a Metadata Record.