A plethora of map-based citizen science sensor platforms for different use-cases already exist. They provide cheap, preconfigured, plug and playable hardware and software solutions. Using data from multiple platforms and resources can be a challenging task in respect of discovering, exploring, downloading and converting. In this paper we present a one-stop-shop for sensor data that tries to tackle these problems. Therefore a basic data schema capable of metadata is established that allows publishing generic sensor platforms and sensor data. For exploration the OpenSenseMap, a web platform is implemented based on common web standards. Citizen science is often called “public participation in scientific research” [1] and describes the engagement by non-professional scientists in collecting and analyzing data, decision making, developing technology and publication of these on a voluntary basis. The idea of involving citizen in scientific projects is not new. Two examples are the Christmas Bird Count [2] and the Galaxy Zoo project, which identifies and classifies galaxies on sky images taken at the Sloan Digital Sky Survey. An always discussed concern about citizen science is data quality [3]. Due to limited knowledge of the volunteers and missing or questionable metadata, scientists often characterise data collected by citizens as valueless. In the beginning citizen science was connected with activities where humans were used as sensors [4]. Nevertheless, the scientific community is becoming more and more interested in citizen science today and citizen science projects are part of complex research projects [5]; e.g. ambient environment monitoring. We think two reasons boosted this trend. First, citizens are getting more interested in their environment and its effects on daily life. Also many popular citizen science projects are related to ambient environment monitoring and topics around smart cities; e.g. the AirQualityEgg project and the SmartCitizen project. Second, the vast development of technology makes it easy and affordable to build the necessary tools for a citizen science project. Microcontroller platforms like Arduino or tessel.io and the quality and price of sensors make it nowadays easy to build sensor platforms, which are easy to use and affordable in price. By using open-source hardware and software, it is easier - especially for traditional non-technical research communities- to create custom sensor platforms. Furthermore, the web makes it easier to share and discuss geospatial data at global scale. This work describes the requirements, design and implementation of the OpenSenseMap. OpenSenseMap is following the clientserver model [6] and its complete application stack is implemented in JavaScript. It describes the basic components and the underlying data model. All components are using open-source technology and are published under an open-source license too. The RESTful service is the heart of OpenSenseMap and implements the data publish and data retrieval functions. Developers may use it to build custom applications around OpenSenseMap or integrate OpenSenseMap into existing projects. The NodeJS application runs its own web server and implements the different HTTP request types. The OpenSenseMap concept is being evaluated with an technical and a user survey.