Chapter 11 Transform Your Map Data

All maps, including interactive web maps, are made up of different layers. These are background basemaps, colored or shaded polygons (also known as choropleth layers), lines, and point data that are often represented as markers.

In this chapter, we will look at multiple ways to convert and edit geospatial data to create layers (files) that you can use in your favorite mapping tools.

We will begin by looking at the process of geocoding, or transforming human-friendly address lines into points that can be plotted on the map (see Figure 11.1 for inspiration). We will then talk about polygons and why you should normalize your data before creating choropleth maps. These map transformations happen inside spreadsheets, so you won’t directly deal with map data until you are halfway through the chapter.

To map addresses, you need to geocode them first.

Figure 11.1: To map addresses, you need to geocode them first.

Before you can dive into creating shapes and dealing with boundaries in the map, we will introduce various file formats (most notably GeoJSON) and talk about geospatial data in general. You will learn that map data can be raster and vector, that geospatial data consists of location and attribute components, and how GeoJSON is different from Shapefiles and other geographical data formats.

You will then get a chance to draw your own map layers on top of satellite imagery using, and learn to simplify, crop, and join spreadsheet and geospatial data in Mapshaper. Both are powerful, web-based open-source geodata tools that for common tasks can substitute for more complex geographic information system tools, such as ArcGIS or QGIS.

By the end of this chapter, you should feel much more confident navigating the overwhelming world of geospatial data.