(Geo)spatial data collection involves assembling all of the spatial data that are to be stored in a computerised format within a geographical information system (GIS). This includes information about the location, shape and attributes of real objects.
Before starting to collect spatial data it's important to establish the following:
Does the same, or similar, data already exist in your organisation, or in the market place?
Gigateway is a free web service aimed at increasing awareness of and access to geospatial information in the UK. The Regional Resource Catalogue also includes geospatial resources.
What is the hypothesis?
Why collect the spatial data and what question do you want to answer?
What level of spatial resolution is appropriate to your application?
The spatial resolution will dictate the accuracy at which a given map scale can depict the location and shape of geographic features. The larger the map scale, the higher the possible resolution. (See Ordnance Survey).
Currency of the data—how long will the data be current?
Is there a process to update it? For example, properties are built and demolished, rendering address data out of date.
Methods of geospatial data capture
Direct (primary) data capture
A primary source of data is where the data can be captured directly into the GIS, such as using Global Positioning Systems, mobile in-field GIS or remote sensing from satellites.
Ground survey
It's possible to create geospatial data by taking measurements direct from physical surveys. While historically paper maps and surveys were important, these days most geographical information is likely to be captured in digital form at the point of initial survey.
Mobile GIS
Mobile GIS is the expansion of GIS technology from the office into the field. A mobile GIS enables field-based personnel to capture, store, update, manipulate, analyze, and display geographic information.
Mobile GIS integrates one or more of the following technologies:
- Mobile devices, such as PDAs or tablet PCs (with appropriate software)
- Global positioning system (GPS) (a system based on satellites that enables users with a receiver to determine the precise coordinates for their location)
- Wireless communications for internet GIS access
It is now even possible to send data captured in the field back to the office in real time.
Remote sensing
Remote sensing involves the use of aerial and space imagery to record geographical information. Through the use of different wavelengths it allows the interpretation of other phenomena such as vegetation type or land use.
Aerial photography
Photographic coverage of the land surface obtained from the air using airplanes, balloons or kites.
Satellite imagery
The capture of satellite images by scanning the earth's surface.
More on primary data
Indirect (secondary) data capture
Secondary sources are, for example, addresses or paper maps. These are usually captured onto the GIS by digitising or scanning.
Scanning
Scanning a map is a straightforward process and generally fast, but it does not provide for the capture of attribute information for features, such as the address of a building. It can also result in large file sizes.
Digitising
Digitising involves passing an electronic cursor over the features of a map. In this way, each of the coordinate points which make up the different shapes can be identified. By clicking the cursor when it is held over a point, digitising captures map data in vector form.
Digitising can be very time consuming because every single point or vertex must be captured individually. When a cartographer is capturing information by digitising, it's possible to attach attribute information to features. Digitising is the main method for creating boundary datasets (administrative areas, functional areas, and so on).
Many different organisations capture their own features and/or boundaries, and some make them available to others. Examples include:
- Ordnance Survey: supplies administrative boundaries, postcode boundaries, and so on(through licensing agreements)
- MAGIC: a web-based interactive map bringing together geographic information on key environmental schemes and designations
Addresses
Addresses are subject to a high level of change from:
- The creation of a new property
- Property redevelopment
- House or street name changes
Within any data set, the quality of addresses will depend on what is asked for, how it is entered, and how the data is reviewed and stored. To be most useful in a GIS, addresses need to be accurate, free of errors, relate to the right place and be regularly updated.
In all cases it is important to ensure that the address data available is sufficient for the project requirements. For example, an address that has adequate information for a letter to be delivered may not have enough detail to enable a fire engine to arrive at the correct destination, such as a ward in a large hospital, in a reasonable time.
The quality of sources of address data can therefore be aided by clear instructions and statements of expectations to the information providers and also through designing in effective quality assurance procedures to eliminate data entry errors.
Addresses are often not collected or stored in a way that makes them easily usable, comparable or geocodable and should therefore be recorded in a usable format or structure—there are no absolute rules on what constitutes a good address, although standards exist that suggest what fields are necessary and what structure the data should take:
- British Standard (BS7666) provides a nationally consistent means of structuring address-based information and a standard format for holding details on every property and street.
- The National Land and Property Gazetteer is the first definitive national (England and Wales) address list providing unique identification of properties and conforms to the British Standard BS 7666:2006 parts 1 & 2.