Introduction to GIS Mapping
Learn more about the basics in chapter one: What is GIS?
GIS software offers a way to manage, organize, and analyze location-based data.
It was originally created in an effort to transcend the limits of paper maps and bring order to unruly data sets: combining the best parts of both.
It should come as no surprise then that the most common application for GIS is mapping.
Mapping and GIS are so closely entwined, it's difficult to consider one without the other. Yes, maps can exist completely independant of GIS. However, without maps, GIS would be little more than a database.
GIS maps add meaning to raw data.
Though a spreadsheet can house huge quantities of data, gleaning insights or understanding is difficult. Render that same data onto a map and, instantly, it becomes easier to both manipulate and analyze.
GIS mapping, like the definition of GIS itself, is categorically quite broad.
In this chapter, we’ll cover mapping basics, traditional GIS map types, and modern maps that expand the definition of GIS. We'll also take a deeper dive into project mappping, one of the newer applications for GIS.
Click any of the topics below to jump there directly.
I. Mapping Basics: Thematic vs. Reference Maps
II. The Wide World of GIS Mapping: A Quick Note
III. Traditional GIS Maps
a. Category maps
b. Quantity maps
c. Heat maps
IV. Modern Maps: Expanding the Definition of GIS Mapping
a. Inspection maps
b. Hazard maps
c. Asset maps
d. Project maps
V. Deep Dive: Project Mapping with GIS
Thematic vs. Reference
Mapping can be divided into two general categories: reference and thematic.
Reference maps focus on location, illustrating natural and man-made features. Good examples of a reference map include street, subway, and topographic.
Thematic maps illustrate spatial patterns and relationships: focusing, as the name suggests, on a theme or particular subject. Population trends, disease rates, and weather patterns are all commonly represented on thematic maps.
That in mind, most thematic maps do use reference maps as their base.
Reference map depicting the streets of London [Source]
Thematic map of soil moisture regimes in the contiguous United States[Source]
For example, you might want to study the relationship between elevation and rainfall in a nearby national park. Using a reference map that outlines elevation as the base layer, you could then overlay annual rainfall data: creating a thematic map.
Remember, GIS is the intersection between data and location.
While you certainly can use GIS to examine a reference map, you'd barely be scratching the surface of its full functionality.
The ability to create thematic maps is what makes GIS truly valuable.
We’ll go over the most common GIS map types - category, quantity, and heat - momentarily. But first, a quick note about the nature of GIS mapping.
The Wide World of GIS Mapping: A Quick Note
As with all aspects of GIS, it's important to remember this:
The umbrella of GIS mapping is massive - covering a wide range of sub-topics.
You can (and people have) written entire textbooks on the subject of GIS.
This variation exists in part because GIS has grown and evolved significantly over time. The GIS maps of today are quite different from the maps you could make when GIS was first released in the early 1980's.
The intent of this chapter is to give you an overview of the most common map types that can be made with both legacy and modern GIS.
First, we'll cover traditional GIS maps: most of which fall under the legacy GIS umbrella. Next, we'll cover maps that are expanding the defintion of GIS mapping, most of which are made with modern GIS platforms.
Traditional GIS Maps
Category maps visualize data categories, as related to specific areas on your map. Examples of category maps include:
- Election results (did the state swing democratic or republican)
- Sales territories (who covers which territory)
- Favorite sport by country
To create a category map, first define your categories and then input relevant data.
Many GIS systems allow bulk data upload, so ideally data entry is fairly quick. After integrating the data, assign a color to each category and watch as the map is generated.
Once you’ve created the map, make changes by manipulating the data directly. For example - if, in the data set, you change Canada to preferring rugby over ice hockey, the color will automatically change on the map.
Quantity maps, otherwise known as choropleth maps, illustrate variations across a defined geographical or political region.
Population density maps are a great example of a quantity map. The one to the right illustrates percentage density of adults ages 20-24 by county in the United States.
Lighter colors represent lower density, and each subsequent darker shade represents higher density.
Often confused with heat maps, quantity maps chart density over non-standard location-based units.
What’s a non-standard location-based unit?
Examples include states, counties, and voting districts i.e. areas with well-defined, but somewhat arbitrary boundaries. This stands in contrast to a standard grid where each area unit is exactly the same.
To make a quantity map, define the area in question, put the data into ranges (0-9, 10-19, 20-29, 30-39), and assign a color to each portion of the range.
Colors in a choropleth map are generally either gradients of one color (light to dark) or diverging colors. Both the numerical ranges and associated colors should be depicted in a legend so viewers can easily understand the map.
Similar to quantity maps, heat maps illustrate density over a given area. However, where quantity maps often illustrate density change, heatmaps generally represent variable intensity within a dataset.
Heatmaps display data over a standardized grid, rather than geographical or political boundaries: using color to illustrate the level of intensity.
Weather patterns occur completely independent of geo-politcal boundaries, so conditions like lightning strikes, drought areas, and large storms are often displayed using heat maps.
Modern GIS Maps: Expanding the Definiton of GIS Mapping
Inspection Maps with GIS
Physical asset inspections occur over large, dispersed territories - making data organization difficult. Take utility pipeline inspection as an example:
There are over 100 million miles of utility pipeline in the United States alone.
Each utility company is responsible for a specific territory: often denoted as a list of addresses. Each address is associated with multiple pipelines, all of which require regular inspection.
Using GIS, utility companies can turn a list of addresses into a digital inspection map.
They can then add relevant data (notes, videos, and photos) to their map as needed. With a digital map, rather than a paper one, data can be reviewed in real-time and important information is easily available to future inspectors.
Hazard maps are used to illuminate areas vulnerable to natural disasters: earthquakes, floods, landslides, tsunamis, etc.
When used properly, hazard maps can help:
- Citizens and planners understand the full scope of potential risk
- Offer insight on which areas are highest risk
- Mitigate the negative effects of catastrophic events (damage, loss of life, etc.)
- Minimize exposure outright through effective planning
- Create plans for effective evacuation sites and routes
An effective hazard map should be easy to understand and created with the intent to facilitate prompt, orderly evacuation.
Asset maps share many similarities with inspection maps.
If anything, they are simply a broader category: one that includes the mapping and management of land, buildings, equipment, infrastructure, electric grids, and more.
The key difference between asset and inspection maps is that asset management and mapping focuses on extending the lifecycle of an asset: managing its maintenance and upkeep so it can stay in use for longer.
Project maps allow an organization to track large-scale physical projects over time. These maps can include features, such as tasks, assets, drawings, and measurements (both area and volumetric).
We’ll look closer at this map type in the next section.
Deep Dive: Project Mapping
A relative newcomer to the field of GIS, project maps allow organizations to track large-scale physical projects over time.
Most legacy GIS platforms can’t accommodate the granular data organization necessary to create an effective project map. However, as GIS technology has evolved, project maps are becoming increasingly commonplace.
As you now know, GIS helps users examine the relationship between data and location: starting with a base reference map and adding layers of data.
Project maps add deep, yet narrow data sets to specific points on the map.
In this context, these points can be any project component: location-based tasks, area measurements, map annotations, and more.
Task management is an integral part of project management.
For non-physical projects, lists, spreadsheets, and whiteboards are effective management tools. Managing a location-based project is much more complicated and GIS helps solve this problem.
Modern GIS platforms give you the ability to assign tasks to specific locations on your map, and then give each task a status.
Some GIS platforms give users the ability to take area and volume measurements within the map itself. This functionality is extremely useful for built-world projects.
Modern GIS gives managers and field teams a way to literally measure project progress.
From site boundaries to stockpile volumes, in-map measurements introduce a level of interactivity that legacy GIS systems don’t often provide.
Like most GIS data types, users can isolate the measurements layer: allowing them to view measurements independently or toggle between layers.
Map annotations have a variety of uses. For project maps, they can be used to outline the site perimeter, mark areas that need attention, and make comments directly onto the map.
Measurements are actually a type of map annotation, but can be considered separately as their application is quite specific.
GIS mapping covers half of what defines GIS as a real-world application.
Remember, we’ve defined GIS here a the intersection between data and location.
Mapping is the location component.
In the next chapter, we’ll cover the other half: data.
GIS data comes in a dizzying array of formats. We’ll be covering important differences between vector and raster data, shapefiles (the most common GIS data type), as well as other useful file formats.