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What, exactly, is GIS?

Unpacking the differences between mere mapping and GIS databases

Geographical Information Systems (GIS) is one of the most mis-understood acronyms we come across. Everyone seems to agree that it GIS valuable, but few can explain precisely what is, and why you should spend money on it.

This article explains what GIS is and how we use it at Advanced Invasives to tackle our clients' problems with invasive non-native plants such as Japanese knotweed and Himalayan Balsam.

Common Confusions

GIS is confusing because it is often used mistakenly to describe four closely related, but distinct things;

  • The merely geographic  - the general approach of viewing problems in terms of their spatial components and spatial relationships.
  • Analysis of GIS the specific analytical techniques used to interrogate spatial problems.
  • Outputs from GIS methods of visualising spatial problems, most commonly maps of some sort.
  • Remote Sensing (RS) - making measurements of the Earth, or other spatial bodies such as the moon or Mars etc, from planes and satellites.

GIS as database

So, what then is GIS?

GIS is the underlying computerised database of the spatial information of a problem, from which all other analysis can then performed.

Think of a visitor map of central London, something like the modern-day Legible London pedestrian map for example;

  • Mapping is the general geographic formulation of the problem (communicating where things are would be grossly impractical in only text form).
  • Walking times to landmarks represent a very basic type of analysis.
  • Maps displayed on the street signage and in printed paper guides are the static images exported from a larger digital 'master-map' resource.
  • The GIS is the database of mapping information underpinning the master map; the mathematical spatial co-ordinates defining polygons, which in the aggregate, form the single layers such as roads, pavements and city greenspaces used across the overall mapping system.

The value of GIS

A simple PDF map of say parks in central London would offer only the most basic geographic understanding of the location, shape and size of the various greenspaces.

A database of the same information is much more valuable because it could be used to reveal relationships with other data. Variation in house prices, localised pollution levels, pedestrian movement densities or types of crime may all have some relationships with parks for example.

So, a GIS database is valuable because once it has is been defined, it provides the baseline from which all other types of analysis can be performed, revealing patterns within and also outside of the dataset.

GIS in the Invasive Species Context

In the context of invasive species GIS is useful because:

  • It provides a baseline reference of the scale and nature of invasive species problems.
  • It reveals the problem at the level of the ecological unit instead of arbitrary land boundaries or divisions of public and private property.
  • It gives all stakeholders an objective, independent way to measure rates of change in invasive species coverage and the efficacy of control methods for politically, or environmentally sensitive projects.
GIS is not always necessary and should not be seen as a default requirement. In some sites immediate priority is simply chemical control of invasive plants. Often this can be organised quickly and pragmatically, just by using simple hand-drawn maps of the target area.

How GIS is created

There are six basic stages to creating and using a GIS asset:

  1. Data capture; remote sensing or field surveying of invasive species coverage on-site.
  2. Master map creation; drawing polygons of invasive species coverage, typically referenced to Ordinance Survey (OS) base data, to create a single authoritative resource.
  3. Spatial analysis; highlighting any important spatial relationships between relevant datasets, typically using a ruleset to grade the relative invasive risk to property.
  4. Mapping; exporting static maps and imagery to visualise analysis.
  5. Handover; once completed, GIS resources can handed over to clients to afford them the ability to manage their invasive species problems in-house and in tandem with their own internal datasets.
  6. Quality assurance; periodic checking of the GIS asset to make sure it is up-to-date and well maintained.

Make it visible

Creating GIS assets is time consuming to undertake; however, this should be weighed against savings made by avoiding ineffectual, repeated cycles of on-site herbicide treatment.

GIS is useful because it makes complex invasive species problems more visible.

We use GIS to take a problem that may be multi-site, multi-stakeholder and seemingly intractable and create a single, tangible resource which can then be used to steer and assess decision-making objectively. Creating a GIS asset also anticipates the need for a common resource, around which future site intervention can be organised.

Using GIS in this manner moves invasives management away from an entirely reactive, fire-fighting approach, that over time is very costly and demoralising, to a pro-active, intentional and utlimately effective strategy.


In combination with more conventional physical or chemical control protocols, GIS offers a more complete approach to long-term invasive species management. GIS can serve as the neutral asset needed to resolve politically sensitive disputes and also meet future requirements for salient ecological information.

The value of GIS should not be under or overstated. Often one can see examples of where GIS is used more to impress than being a necessary tool for the problem at hand.

At Advanced Invasives we use GIS sparingly, where it brings clarity to an especially challenging invasives problem and because it helps our clients organise and save money on long-term control strategy.