Data collection involves assembling all of the spatial data that are to be stored in a computerised format within the geographical information system (GIS).
Before starting to collect spatial data it is important to establish the following:
- Does the same, or similar, data already exists in your organisation, or in the market place? Gigateway is a web service aimed at increasing awareness of and access to geospatial information in the UK. The WMRO Resource Catalogue also captures 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 For example, properties are built and demolished, rendering address data out of date.
Primary data
A primary source of data is where the data can be captured directly into the GIS, such as Global Positioning Systems or remote sensing from satellites.
Remote sensing
The process by which satellite images are created by scanning the earth's surface.
Global Positioning Systems (GPS)
GPS is a system based on satellites that enables users with a receiver to determine the precise coordinates for their location.
Aerial photography
Photographic coverage of the land surface obtained from the air using airplanes, balloons or kites.
More on primary data
Good practice: Remote sensing and aerial photography
Computer Processing of Remotely-Sensed Images - An Introduction by P.M. Mather, 2004, 3rd Edition
Secondary data
Secondary sources are, for example, addresses or paper maps. These are usually captured onto the GIS by digitising or scanning.
Quality of addresses will depend on what is asked for and how, how it is entered, and how the data is reviewed and stored. Addresses need to be accurate, free of errors, to the right place and regularly updated.
The address needs to be sufficient for requirements. 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.
Source data quality can be aided by clear instructions and statements of expectations to the information providers.
The address should be recorded in a usable format or structure. Addresses are often not collected or stored in a way that makes them easily usable, comparable or geocodable. The information collection processes should be designed with effective quality assurance procedures to eliminate data entry errors.
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 aims to be the definitive national address list providing unique identification of properties and conforms to the British Standard BS 7666.