Hands-On Data Visualization

Chapter 13. Transform Your Map Data

In Chapter 7, we introduced basic concepts about interactive web maps, which are made up of different data layers. When users explore an interactive map, they usually click on the upper layer, which often displays some combination of points, polylines, and polygons on top of a seamless set of basemap tiles that are built from raster or vector data. Whether you create maps with drag-and-drop tools, such as Datawrapper (see “Choropleth Map with Datawrapper”), or customize Leaflet map code templates (see Chapter 12), you may need to transform data to work with one of these types of map layers.

In this chapter, we’ll delve further into geospatial data and its different formats, such as GeoJSON, the open-standard format most commonly used in this book (see “Geospatial Data and GeoJSON”). You’ll learn how to find and extract geographic boundary files in this format from the crowdsourced OpenStreetMap platform in “Find GeoJSON Boundary Files”. We’ll show how to convert or create your own top-level map layer data using the GeoJson.io tool in “Draw and Edit with GeoJson.io”, and how to edit these layers with spreadsheet data using the Mapshaper tool in “Edit and Join with Mapshaper”. You’ll also learn how to georeference a high-quality static map image and transform it into interactive map tiles using the Map Warper tool in “Georeference with Map Warper”. All of these free, web-based geodata tools are easy to learn, and in many cases they replace the ...