Sapelli is an open source suite of data collection and sharing tools for android smartphones or tablets, and is used primarily for mapping. It has been developed by the Extreme Citizen Science (ExCitesS) research group at University College London to enable illiterate indigenous communities to engage in citizen science. This suite of tools currently includes Sapelli Launcher, Sapelli Collector and Sapelli Data Sender. The applications can be downloaded from the Sapelli website.

Sapelli’s unique features include:

  • The use of pictorial decision trees using an icon-based interface to enable data collection by illiterate communities.
  • A data transmission system designed for remote areas where network connectivity is unstable, slow or expensive.

Sapelli has the following strengths and weaknesses for community-based forest monitoring:


  • Participatory software development enables communities to develop a data collection model that meets their needs
  • Icon-driven interface empowers illiterate users
  • Data can be transferred in compressed form in areas with poor network connectivity
  • Open-source


  • Designed to be used as part of participatory problem solving approach to resolve specific local issues rather than to address externally driven monitoring needs such as above-ground biomass
  • Data analysis, visualisation and reporting functions for communities are not available (at the time of publication of this summary)
  • Building and modifying decision-trees requires technical knowledge or the involvement of external facilitators
  • Has a small user base than other tools such as ODK and thus a smaller support community for troubleshooting
  • Requirements include android phones, power for charging phone batteries, and network connectivity to transfer data

Sapelli is designed to be used as part of a participatory problem solving approach with local communities to address specific issues. The participatory development of the Sapelli software, such as the decision trees and icons, is part of a wider participatory process that includes free, prior and informed consent (FPIC), problem framing and the development of community protocols for engaging with projects and their other stakeholders (e.g. companies, government).

Whilst Sapelli users do not need any previous information and communications technology (ICT) experience, a high level of expertise, including a basic knowledge of code, is required to design and modify pictorial decision trees. Users are therefore reliant on the engagement of project facilitators for development of software.

The Sapelli data collection app uses hierarchical, pictorial decision trees to allow users to collect GPS points. Text, numbers, checkboxes and radio buttons can also be used for data input where appropriate. In each step of the decision tree up to six icons can be used. These can be literal, categorical or metaphorical (Figures 1 and 2). Auxiliary data can also be recorded as photographs, audio files and videos.     

sapelli screen
Figure 1. Up to six images can be displayed on the screen

sapelli icons
Figure 2. Sapelli icons

The decision-trees and icons are co-developed with the communities in a participatory process. Icons and decision trees can be rapidly modified in response to feedback during this process. However, currently there is no form creator application to support the design of these decision trees without modifying an XML form, which requires literacy and technical knowledge.

To support illiterate users to collect data, Sapelli Launcher can be used to replace the standard user interface on a smart phone with a text-free user interface. Sapelli Launcher can also be used to specify what apps are allowed on the phone and to enable a password protection function which may be important where data collection is sensitive.

Data can be submitted via binary, compressed SMS  messages, or by HTTP via cellular or Wi-Fi networks. This flexibility supports data submission in remote areas in tropical forests, for example, where cellular or Wi-Fi networks are not available. The Sapelli Data Sender (a mobile phone app) automatically checks for connectivity and, based on the available networks and bandwidth, the data is transmitted by SMS or HTTP. Data sent by SMS is compressed and sent to another smartphone with Sapelli installed. Received data can be exported from the smartphone or transferred to the cloud.

Data analysis and visualisation features are currently being developed. Planned features include a web-interface for survey design (Decision Tree Authoring Tool), project management, and querying, analysis and visualisation of data (Sapelli Maps).


  • Cyber Tracker is also focussed on icon-based approaches
  • ODK

How can I learn more?

Sapelli can be downloaded from the ExCiteS research group website. Tutorials are being developed on the Sapelli wiki pages. Sapelli can be found as an open source project on GitHub.

Related Initiatives:



Open Source 
Phone Network 
Smart Phone 
Level of Expertise