This page lists free, in the monetary sense, tools, data and other resources for making maps. Although I’m concentrating on open source, open licensed materials, not everything given here meets that criteria. So check the individual licenses before use, and be aware that dependencies may not be open.
General resources
Bamboo DIRT: DIgital Research Tools catalogue, section for cartographic tools: site defunct but archive can be found on the Wayback Machine: https://web.archive.org/web/20181210160024/http://www.dirtdirectory.org/categories/mapping
Debian GIS: Packages for the Debian Gnu/Linux distribution. http://wiki.debian.org/DebianGis
Ubuntu GIS: Software for the popular linux distro Ubuntu and its many variants. https://wiki.ubuntu.com/UbuntuGIS
Online Services:
MapMe: Free to use online map annotator, with crowd-sourcing possibilities. http://mapme.com
Qgis Cloud: Free and paid-for map hosting using the best known open source mapping software. https://qgiscloud.com/
Doogal Batch Geocoding: Uses Google Map data; produces a nice map as well as co-ordinates in a number of formats. https://www.doogal.co.uk/BatchGeocoding.php
Batch Geocoder: More bulk geocoding. https://geocode.localfocus.nl/
Tools
MapsData Online Converters: An array of online tools – free to use but not open source – for converting data into co-ordinates etc. http://www.mapsdata.co.uk/online-file-converter/
Open Layers: An open source javascript library to load, display and render maps from multiple sources on web pages. http://openlayers.org/
QGIS: The opensource alternative to the likes of ArcGis. http://www.qgis.org
MapWarper: for geo-correcting old maps, and lining them up with modern maps. http://mapwarper.net/
Story Map JS: “A free tool to help you tell stories on the web that highlight the locations of a series of events.” http://storymap.knightlab.com/
ThenMap: a repository, API and Javascript library for historical borders. http://www.thenmap.net/
Things to do with postcodes: Tools and documentation for doing things with UK postcodes. Note new URL! https://www.getthedata.com/postcode Also available as data and API.
Temporal Mapping Tools
For combining time and space. And yes, most of these tools are called Timemap.
Neatline: Geotemporal exhibit-builder for the Omeka web-archives platform. http://neatline.org/
Timemap.js: Javascript library to help use a SIMILE timeline with online maps including Google, OpenLayers, and Bing. http://code.google.com/p/timemap/
TimeMapper: From the good folk at the Open Knowledge Foundation, Timemapper “lets you create elegant and embeddable timemaps quickly and easily from a simple spreadsheet.” Requires a Twitter account and Google spreadsheets. http://timemapper.okfnlabs.org/ Introductory tutorial: http://okfnlabs.org/blog/2013/10/11/timemapper.html
Data
Atlas of Historical County Boundaries: Shapefiles for the United States. Licensed under CC-BY-NC-SA. http://publications.newberry.org/ahcbp/index.html
Open Street Map: Crowd-sourced map of the world, under a free license, with a veritable ecosystem of tools and projects based upon it. http://www.openstreetmap.org
Amsterdam Open Geo Data: Amsterdam Open Geo Data
Historic Maps
Antique Maps of Iceland: Some 770 maps, all available for download. http://islandskort.is/en/
Brighton: Historic maps of Brighton, nee Brightelmstone, from the late eighteenth century on. https://dams-brightonmuseums.org.uk/assetbank-pavilion/action/browseItems?categoryId=1929&categoryTypeId=1 [Dead link.]
British History Online: Maps of London and Ordance Survey maps from the late c19th. https://www.british-history.ac.uk/catalogue/maps
Grub Street Project: Many historic maps of London. https://www.grubstreetproject.net/london/maps/
Harvard Geospatial Library: Lots of content, including geo-rectified maps. But an interface both dreadful and undocumented. There’s riches here, but you have to work damned hard to pull them out. http://hgl.harvard.edu:8080/opengeoportal/
See also the brief intro (not linked to from the actual site): https://library.harvard.edu/services-tools/harvard-geospatial-library
ICGC Cartoteca Digital: Large collection of well digitised maps from a Catalonian collection, but sadly licensed under a no derivatives CC license. Downloading seems to require logging in. http://cartotecadigital.icc.cat/cdm/
Library of Congress: Many maps, many of very high quality, and freely downloadable and reusable. https://www.loc.gov/maps/
LSE Charles Booth Poverty Maps: Available in high quality reproductions from Flickr.
National Library of Scotland: Many maps, mainly of Scotland and the rest of the British Isles, including early Ordnance Survey maps. http://maps.nls.uk/index.html
See also their data repository: https://data.nls.uk/data/metadata-collections/
New York Public Library: Many high-quality public domain maps in their digital collection: http://digitalcollections.nypl.org/ See also their geo-corrected versions: http://maps.nypl.org/warper/
Peliagos Project: Medieval maps, atlases, charts and itineries, hosted by the British Library. https://data.bl.uk/pelagios/
Perry-Castañeda Library Map Collection: Many maps, albeit of varying quality. http://www.lib.utexas.edu/maps/historical/
Rumsey Collection: Very large, and generally very well digitized, collection of maps spanning the whole planet. Many maps downloadable and in public domain or Creative-Commons-licensed; but no way I can see of downloading geo-referenced ‘warped’ maps. http://www.davidrumsey.com/
Wikimedia Commons: Many freely licensed maps. http://commons.wikimedia.org/wiki/Category:Maps.
Other Resources
Map Icons Collection: Fantastic collection of CC-BY-SA licensed icons. Now hosted by Mapmarker. https://mapicons.mapsmarker.com/
Maki: More map icons, this set from Mapbox: https://www.mapbox.com/maki/
Last updated 17 January 2023. This list is public domain, and may be freely adapted for any purpose whatsoever.