User:Adavidson/test/section2 1
II. Basics
II.1 OpenStreetMap
This subchapter will help you to gain a good understanding of the subject areas of the present work by answering basic questions on the understanding of the open geodata-based OpenStreetMap project supported by an online community: What does "free" mean in this context? What are geodata? What is an online community? Then the origins and importance of the project, the techniques used to implement it (server architecture, rendering and display techniques, editing tools), the underlying data model, and the ways of communication and documentation in the project are explained.
A Free Content, Geodata and Online Communities Free Content - commonly referred to by the English term Open Content - are creative works (films, photos, music, lyrics, etc.) that are released either royalty-free or under copyright licenses, primarily their own allow free and free use - ie permit their use, transfer and processing, even in a commercial manner (Mantz, 2007, Möller, 2006). The driving thought and goal at the same time is to make creative works available to all people, as restrictive copyright restrictions often inhibit the dissemination and thus the exchange of knowledge and ideas. In addition, the free and rapid availability of information (eg from scientific publications) particularly makes use of research and teaching at universities (Eidenberger & Ortner, 2007, Möller, 2006). In order for content to be considered free, either their authors must grant them a free license or they must be public domain (license-free). This is the case in many states (including Germany) only after expiration of the copyright protection periods. In contrast to the legal systems of other states, the legal system of the United States even provides for a complete renunciation of copyright by the authors, which enables them to achieve the status of the public domain for their works from the beginning (Möller, 2006). On the other hand, if authors want to use an open-content license, they have various options available to design them for their own purposes and to formulate them according to their own ideas. According to Möller (2006), the most widely used open content licenses are those of the Creative Commons (CC), an American non-pro fi t organization that provides easy-to-understand, legal license texts. Here, different combinations of conditions of use can be selected ("assembled") that yield a suitable CC license for the work to be protected (Eidenberger & Ortner, 2007). These conditions permit or prohibit the use of the work for commercial purposes and determine whether any edits under the same license as the work itself must be passed (whereby the principle of Copylefts - preventing the unfree collection of a work - enforced) or not. Common to all combinations is the obligation to name the author / author (ibid.). The most important and well-known example of a collection of open content is, according to Danowski and Voss (2005), the existing Wikipedia since 2001, a volunteer-created and continued international project to create a free Internet encyclopedia that is available in a variety of language versions is and includes several million keywords.
Geodata is digital data that represents real or abstract objects that are spatially related to a position on the surface of the earth and are therefore called geo-objects. This property is referred to by the synonyms geo reference, georeference or simply spatial reference and can be present in direct or indirect form. A direct spatial reference characterizes that the positioning of the objects on the earth's surface is described by the assignment of coordinates. Indirect spatial reference, on the other hand, refers to other geo-referenced information, such as an administrative unit (Bill & Zehner, 2001, Bollmann & Koch, 2001/02). According to Bartelme (2005), geo-objects are represented by geodata that always have structural, geometric and often additional thematic (content) attributes (properties). According to Bollmann and Koch (2001/02), the geometric attributes include the following areas: • geospatial position: information about the spatial reference (eg coordinates dependent on the system used), • geometric shape: resulting from the geospatial position, • spatial dimension : dimensionless (point), one-dimensional (line), two-dimensional (area), two and one-half dimensional (surface) or three-dimensional (body), and • topology: positional relationships of the objects to each other (eg neighborhood), based on the three topological categories nodes, Edge and stitch. The data structure on the basis of which the geometric properties are modeled depends on their later intended mapping as raster or vector graphics. In terms of their origin, geodata may be either primary data obtained directly from data collections or secondary data derived from primary data (Bollmann & Koch, 2001/02). The individual, uniquely identifiable "portions" of geodata (entities) and their relationships (relations), which mostly derive from the topology, are often described by the entity-relations model, according to Bartelme (2005). In this case, entities that have the same properties, shapes, and topology requirements are grouped into entity classes (types), which can also be linked by relations.
An online community is a usually democratically organized communi- cation community of people who meet each other via the Internet. It serves as a platform for the exchange of opinions and experiences via Internet forums, such as mailing lists or web forums, but must not be equated with these techniques, but must be perceived as a social phenomenon (Eigner, 2003). In order for an online community to be maintained, it needs the care and support of community members (ibid.). Net communities allow their members to quickly open up many other stakeholders who are deeply interested in and specialize in a particular topic. As a result, such members tend to join together in groups that cooperate to achieve a common goal (Danowski & Voss, 2005, Ebersbach et al., 2008).
B Emergence and Significance of the OpenStreetMap Project OpenStreetMap, an international project for the acquisition and provision of free map data started in 2004, marks a point of contact between geodata, free content and network communities (Ramm & Topf, 2009). For this purpose, geodata are collected, which are then stored under an open-content license in a central database in order to be used in many ways. The most important use of the data is derived from them, interactive Web map display, which can be reached under the URL http://www.openstreetmap.org (as of March 16, 2009). The OpenStreetMap project makes it possible for all interested people to contribute as volunteers, either by themselves collecting new geodata for the project or by expanding, modifying or improving existing data. The participants are organized as an online community that provides various methods for communication and documentation as a platform, but also organizes personal meetings of the participants (ibid.). The copyright license under which the data resides in OSM is the Creative Commons Attribution-Share Alike license (CC-BY-SA), which governs the use of the Creative Commons Attribution-Share Alike. Editing, copying and distribution of the data (also for commercial purposes) is permitted if the author / creator is named and the product is published under the same or a compatible license. However, it has been shown that CC-BY-SA is only of limited use for OSM (and geodata in general), as it has some uncertainties. Thus, according to Ramm and Topf (2009), it is a problem that not all the OpenStreetMap project as a whole, but all the collectors are in particular rights holders of the geodata and should always be mentioned as such when they are passed on. However, since this is virtually unmanageable, the license is designed so that the continued use of the data will be sufficient to indicate that the community of OSM participants is the rights holder. Moreover, according to Fairhurst (2008), Fairmoor's OSM data (2008) are factual or demonstrable factual facts for all people and, as a whole, constitute a collection of data rather than a creative work, making them a database work in the copyright sense. However, the change of the existing license CC-BY-SA would be very costly, since this would require the approval of all previously active participants in OSM. Nonetheless, there is a plan within the community to migrate to the Open Database License (ODbL) for database sites based on European Union (EU) database law. Although this would protect the compendium, but not the single geodata, which would require as factual fact another license in addition to the ODbL, for example, the Factual Information License (FIL, dt license for factual facts), which is in discussion for this. Using the FIL would recognize that geodata is not worthy of protection: a situation that remains controversial in many national legal systems, especially within the EU (Ramm & Topf, 2009). According to Ramm and Topf (2009), there are basically two possibilities for gathering data for OSM: self-registration or import from external sources, which are made available to the project. Autonomous acquisition can be realized using two techniques: On the one hand, by means of receivers of data from the Global Positioning System (GPS), waypoints or tracks can be recorded and subsequently processed; on the other hand, data sources such as released aerial and satellite images or even orthophotos can be used for digitizing. The direct import of previously converted geodata from external and freely available or provided sources is less common. Changes to the existing data can be traced at any time based on a change history and assigned to the community members. Restoring earlier versions and directly comparing changes (as is possible, for example, in Wikipedia) are so far difficult to achieve, as the entities are too closely linked to each other to isolate and, if necessary, undo individual changes in isolation. Finally, to underline the importance of OpenStreetMap beyond the boundaries of the project website, there are some applications based on the OSM geodata: a winter sports map with ski resorts and ski lifts (like the OpenPisteMap accessible at http://openpistemap.org ) As of March 17, 2009), a map that allows comments to be made on OSM without immediate removal (such as the OpenStreetBugs available at http://openstreetbugs.appspot.com , as of March 17, 2009), Equestrian and hiking maps (like the riding and hiking map available on http://opentiles.com/nop , as of 17 March 2009) and many more. Furthermore, the data are also suitable for route calculations or navigation with mobile devices (Ramm & Topf, 2009).
C Technical implementation of the OpenStreetMap project According to Ramm and Topf (2009), the data for OpenStreetMap are managed in a database with several tables on a central server using the free, object-relational database management system PostgreSQL (see Fig. 2). 1). The GPS raw data (tracks and waypoints) are stored as primary data and the geo data prepared on the basis of this as secondary data. The requests (read and write accesses) to the database are made via an application programming interface (API), which controls both external accesses and those of the other OSM components and is referred to as the OSM protocol (cf. Fig. 2-1). In order to use the geodata for further processing, these can either be downloaded directly via the described API - which is only possible with a limited data extract per request - or a dump (dump) of all geodata from the database can be used ( see Fig. 2-1), which is provided weekly. The most important OSM components according to the database are the rendering systems and tile servers, which according to Ramm and Topf (2009) are necessary for the presentation of the web map display (see Section B). Rendering systems use the geographic data available as vector graphics for several zoom levels to calculate different, equally sized, square raster graphics, so-called tiles, which Tile servers keep ready for access. These tiles are designed for ease of use of the Web map display, as they speed up the loading and construction of the map image in the web browser. The most important rendering system for OSM is Mapnik, because it provides the default view of the OpenStreetMap web map display. The basis for the rendering is the weekly dump of the geodata (see Fig. 2-1). Another rendering system for OSM is Osmarenderer, which exploits the Tiles @ home project (see Figure 2-1). Here, the tiles are calculated on distributed clients by means of Osmarenderer and then centrally held on a Tile server for the access. However, Osmarenderer can not generate raster graphics directly, but instead creates files in the format Scalable Vector Graphics (SVG) from the geodata, which a separate SVG renderer then converts to raster graphics. To display the rendered OSM map graphics on the client (ie in the web browser), use a Slippy Map ("fl inke" map) based on OpenLayers, a free JavaScript library for the dynamic display of maps in the web browser. Among other things, it offers the possibility of changing the scale (the zoom level) of the map image and moving the map section (Ramm & Topf, 2009). To make changes to the existing OSM data or to add new ones, there are two categories of editing tools: o ffl ine and online editors. The most important editor is the JOSM software written in the Java programming language, which provides all the necessary editing functions and can be extended by numerous plug-ins. The most widely used online editor is Potlatch, an editor embedded in the OpenStreetMap website, based on the Adobe Flash development environment, which has fewer features than editorial editors, but is more intuitive to use (Ramm & Topf, 2009). ,
Potlatch client
Slippy Map
Tile server tile server
Tiles @ home Osmarenderer
mapnik
OSM log dump
Database server
PostgreSQL database
Fig. 2-1 Building and Interoperating the OpenStreetMap Components
D OpenStreetMap data model According to Ramm and Topf (2009), entities of geospatial data in OpenStreetMap are referred to as map features, are unambiguously described by an identi fi cation designation (ID) and, in addition to their inherent structural properties, include geometric and geometric features thematic attributes. The thematic attributes are described by tags, which consist of a key and a value, always apply to the whole entity (never to a part of it), always as strings exist and can occur in any number per map feature. Keys and values may be chosen arbitrarily - there are no defined attribute lists. This also means that the spelling and the wording of the keys and values can be chosen arbitrarily. However, in a continuous process (in terms of its frequency of use), those keys and values that appear most appropriate to the community prevail. For these, English terms are always used to ensure their international understanding in the community. The geometric attributes are described for each map feature either by nodes (German interpolation points), Ways (German Linienzüge) or Relations (German relations). Nodes consist of details of their coordinates and their last processing; they can serve as support points for the course of linear or surface entities, or they can occur in isolation as points. Ways consist of an ordered list of at least two nodes (and thus have a direction) as well as details of their last processing. They are used for linear entities, or planar ones, if the first and last node in the list are identical and there is a corresponding tag that identifies the Way as a surface. Relations consist of information about their last processing and an ordered list of their members (dt members) in any number together with their respective role (Ger. they are used to model topologies and their members can be nodes, wishes or other relations. The topological data model described above (see Fig. 2-2) is based both on the organization of the OpenStreetMap database and the OSM data exchange format, or more precisely on the data schemas that are required in each case (Ramm & Topf, 2009). According to Bartelme (2005), the difference between the data model and the schema lies in the fact that the latter is the concrete, textually and graphically formally expressible variant of the former. A data schema thus includes the structure of the data, its contents and the rules that apply to it.
geometric attributes
consists
is base of
2 ... n 0 ... n 0 ... n
0 ... n
node
0 ... n 0 ... n Relation Way 0 ... n 0 ... n 1 1 1
0 ... n 0 ... n
Day (Key + Value)
0 ... n
thematic attributes
Fig. 2-2 Topological model of the OpenStreetMap geodata (Source: Ramm & Topf, 2009, p. 50, modified)
The data exchange format used by the OSM community is the so-called OSM XML format, which is based on the text-based, man-machine readable Extensible Markup Language (XML). According to Kemp (2008), with the metalanguage XML it is possible to de fi ne own application-specific languages and tree-like document structures, the OSM XML format can also be called an XML dialect. The introductory XML declaration is followed by the root element <osm> and hereafter a list of entities, listing first all nodes and then all the ways and relations. Optionally, a <bound> element can be used that specifies the area of the earth's surface containing all the entities listed in the document. The version attribute of the root element always specifies the version of the OSM protocol and thus the version of the OSM XML format used (Ramm & Topf, 2009). By way of example, an excerpt from an exemplary OSM XML file is shown below - with a butcher's shop as a node, a main road and a lake as linear and area-like ways, and a boundary course as a relation to the representation of its property as an island polygon:
<? xml version = '1.0' encoding = 'utf-8'?> <osm version = '0.6' generator = 'OpenStreetMap server'> <bounds minlat = '- 33' minlon = '92 'maxlat =' - 32 ' maxlon = '93 '/> <node id = '42' lat = '- 32.8739031' lon = '92 .7248729 'user =' mumpitz 'timestamp =' 2008-08-08 08:08:08 'visible =' true '> <tag k = 'shop' v = 'butcher' /> <tag k = 'name' v = 'Butchery Butcher' /> </ node> ... <way id = '442' timestamp = '2006-11-11 04 : 55: 21 'user =' mumpitz 'visible =' true '> <nd ref =' 24242 '/> <nd ref =' 87252 '/> <nd ref =' 24215 '/> <nd ref =' 83857 ' /> <day k = 'highway' v = 'secondary' /> <day k = 'maxspeed' v = '70 '/> </ way> <way id = '27' timestamp = '2008-03-12 07 : 59: 11 'user =' mumpitz 'visible =' true '> <nd ref =' 31492372 '/> <nd ref =' 31492338 '/> <nd ref =' 31492369 '/> <nd ref =' 31492372 ' /> <day k = 'natural' v = 'water' /> <day k = 'name' v = 'Water Lake' /> </ way> ... <relation id = '120022' timestamp = '2009-02-22 08:29:21 'user =' mumpitz '> <member type =' way 'ref =' 2878061 'role =' outer '/> <member type =' way 'ref =' 8125153 'role =' inner '/> <tag k = 'type' v = 'multipolyg on '/> <tag k =' boundary 'v =' administrative '/> <tag k =' admin_level 'v =' 6 '/> </ relation> ... </ osm>
The spatial reference of the OSM geodata is directly produced by a spherical polar coordinate system, namely geographic coordinates (latitude and longitude) using the World Geodetic System 1984 reference system (WGS 84) as the geodetic datum, which is also the geodetic basis of the GPS (Ramm & Topf, 2009). The geodata are stored only two-dimensional, which is why so far no height information in OpenStreetMap are stored.
E Communication and documentation in the OpenStreetMap project The most important communication platforms provided by the OpenStreetMap community are Internet forums, namely various web forums and mailing lists. With regard to the former, especially the one that can be reached at http://forum.openstreetmap.org (as of 16 March 2009) is divided into different topics and national user groups and a place for the exchange and archiving of opinions Representing knowledge and experience. However, the mailing lists, which are also subdivided into subject areas and national user groups, are more important and more widely used within the community. The documentation of the OpenStreetMap project is not only available on the Internet forums, but also in a specially created wiki, a system which, according to Danowski and Voss (2005), makes it possible to view and modify textual content online. The OpenStreetMap community uses the wiki primarily to discuss and document procedures for capturing and modeling map features. On individual wiki pages, possibilities for the development of tags are proposed, discussed and finally subjected to a vote, the outcome of which decides on the widespread acceptance of the tags. However, the tags can still be chosen arbitrarily and are subject to occasional changes and improvements through a continuous discussion process, which is why the wiki should not be seen as the modeling guide, but merely as a modeling aid (Ramm & Topf, 2009). Summary: OpenStreetMap OpenStreetMap is a project for the extraction and provision of free geospatial data under a Creative Commons license. These are usually recorded by the project participants - the OpenStreetMap community - by means of GPS receivers and subsequent processing of the raw data and stored in a central database, the most important technical component of the OpenStreetMap project. To display the geodata present in vector format as a pixel-based map in the web browser, the rendering systems required for this either access the database directly via a programming interface or use a regular dump of the database. In addition to the interactive web presentation of the world map, which functions as an editing interface, at http://www.openstreetmap.org (as of March 16, 2009), a large number of other applications based on OpenStreetMap geodata still exist. The topological data model on which the OSM data is based provides, for each described geo object, a map feature whose geometric properties can be expressed either as a node (two-dimensional geographic coordinate), Way (a multi-node line or area), or relation ( for the modeling of topologies). The thematic attributes of each map feature are described by one or more tags, each consisting of a key and a corresponding value, both of which can be chosen arbitrarily. The communication within the OpenStreetMap project takes place in Internet forums, the documentation in a wiki.