Chapter 14 Transform Your Map Data

TODO: clean up intro

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 strategies to geocode large datasets, such as 10,000 addresses, with US Census tools. 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.

With our tutorials, you will learn how to convert or draw your own layer of map polygons or polylines on top of satellite imagery using the GeoJson.io tool, and also how to edit geospatial data and join it with spreadsheet data using the Mapshaper tool. 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, a Windows-only de-facto industry standard in geospatial software, or QGIS, a free and open-source alternative available for Mac, Linux, and Windows. Finally, you’ll also learn how to georectify a digitized map to display as a background overlay using the MapWarper tool.

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