Once you've selected your datasets there's a wide range of different tools available to help you query, convert, and analyse the data.

Quick visualisation and data format conversion

• GeoJSON.io: A simple website for that allows for uploading, converting, and visualising moderately sized spatial datasets. You can also draw and create your own spatial datasets - handy for creating dummy datasets!
• Ogre: A handy website to convert many common spatial data formats (including shapefiles) to the modern GeoJSON format.
• NationalMap: NationalMap is not only a handy catalogue of government datasets, you can also upload and visualise other datasets on it (supports common formats like GeoJSON, KML, GPX, and more).

Platform as a Service Maps

• Carto (formerly CartoDB): A simple, easy-to-use platform for everyone (not just geospatial nerds). Upload your data, hook into common datasets (e.g. country borders, administrative boundaries), and create beautiful web and mobile maps right from your browser.
• ArcGIS Online: Make and share beautiful maps, and do everything in between. Maps, apps, analytics, administration, collaboration through an easy-to-use mapping solution.
• MapBox: Mapbox is a mapping platform for developers. Easily integrate location into any mobile or online application. Search, geocoding, real-time data, directions and routing, 2.5D and 3D maps.

Desktop software

• QGIS: The open source Geographic Information System. Create, edit, visualise, analyse, and publish geospatial information on Windows, Mac, Linux, and BSD.
• ArcGIS Pro: ArcGIS Pro reinvents desktop GIS. Design and edit in 2D and 3D, work with multiple displays and layouts, and publish finished web maps directly to ArcGIS Online or Portal for ArcGIS, connecting you to users throughout the world.

Databases

PostGIS: Spatial databases aren't just for storing data - they're great for conduct complex analysis tasks if you're happy writing SQL queries. For spatial databases consider nothing but the best: the PostGIS extension to PostgreSQL. If there's a spatial query or manipulation you need to do then PostGIS has it; and hundreds of other functions besides. It's easy to get PostgreSQL + PostGIS running quickly on macOS, Windows, or AWS.

Command-line

GDAL: Check out GDAL (Geospatial Data Abstraction Library), which has readers and writers for over 50 types of spatial data. GDAL bindings also exist in Python, .NET, et cetera.

Web & mobile mapping libraries

• CARTO.js (formerly CartoDB.js): CARTO.js is a simple unified JavaScript library that interacts with the CARTO Engine service. This library enables you to connect to your stored visualizations, create new visualizations, add custom interaction, and access or query raw data from a web browser.
• ArcGIS for Developers: Bring the power of location to your apps with ArcGIS – a mapping platform accessible to developers. Create and manage geospatial apps regardless of your developer experience. Build web, mobile, and desktops apps that incorporate mapping, visualization, analysis, and more. ESRI also has an awesome GitHub portal for developers.
• OpenLayers: A high-performance, feature-packed library for all your web mapping needs. OpenLayers makes it easy to put a dynamic map in any web page. It can display map tiles, vector data and markers loaded from any source. OpenLayers has been developed to further the use of geographic information of all kinds.
• Leaflet: Leaflet is the leading open-source JavaScript library for mobile-friendly interactive maps. Leaflet is designed with simplicity, performance and usability in mind. It works efficiently across all major desktop and mobile platforms.
• Google Maps JavaScript API: Start with the maps your users love, add the data developers trust. Build a custom map for your site using styled maps, 3D buildings, indoor floor plans, multi-modal directions and more.
• MapBox for Developers: Mapbox is the mapping platform for developers. Build maps and applications on our simple and powerful APIs, and use our open source libraries for interactivity and control.