What is GIS mapping?
GIS mapping is a process that helps users manage, organize, and analyze location-based data.
Combining traditional mapping with location-based data, it was created in an effort to transcend the limits of two-dimensional paper maps.
Learn more about the basics of GIS in part one: What is GIS?
GIS mapping adds
meaning to raw data.
Spreadsheets can house huge quantities of data, but gleaning insights is difficult. Render that same data onto a map and, instantly, it's easier to analyze and manipulate.
Like the definition of GIS itself, GIS mapping is categorically quite broad.
In this chapter, we’ll cover mapping basics, traditional GIS map types, and modern maps that are expanding the definition of GIS.
Click any of the topics to jump there directly.
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 reference maps include street, subway, and topographic.
Thematic maps illustrate spatial relationships: focusing, as the name suggests, on a theme or particular subject. Population trends, disease rates, and weather patterns are all often represented with thematic maps.
That said, most thematic maps do use reference maps as their base.
For example, say you're curious about the relationship between elevation and rainfall in a nearby national park.
You would start with a reference map that outlines elevation and then overlay annual rainfall data: creating a thematic map.
Creating thematic maps is where GIS shines.
You absolutely can use GIS software to examine a reference map, but you'd barely be scratching the surface of what that program can do.
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.
As with all aspects of GIS, it's important to remember:
GIS mapping is a massive category and spans a wide range of sub-topics.
People can (and have) written entire textbooks on the subject of GIS.
This variation exists, in part, because GIS has evolved significantly over time. GIS maps today are quite different from those you could make when GIS was first released in the early 1980's.
This chapter will give you an overview of the most common map types you can make with both legacy GIS, as well as more modern platforms.
Category maps visualize data categories, as related to specific areas on your map. Examples of category maps include:
To create a category map, 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 a state from Democrat to Republican, 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.
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.
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.
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.
With a digital mapping, as opposed to paper, data can be reviewed in real-time. 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:
An effective hazard map should be easy to understand and created with the intent to facilitate prompt, orderly evacuation.
GIS mapping covers half of what defines GIS as a real-world application. Remember, we’ve defined GIS here as 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 cover the differences between vector and raster data, shapefiles (the most common GIS file format), as well as other useful GIS data types.