A map consists of a base map and a number of additional layers. You can use ArcGIS for Desktop software and/or ArcGIS Online to create a map with layers. First you add the base map yourself (personal data) or download it from the internet (open data). Next, you can add extra layers to your base map after which the map can be used for further analysis. You can create data yourself with the available geoprocessing tools, or download it from the internet – after critically assessing it.