Web Mapping is the process of designing, implementing, generating, and delivering maps on the World Wide Web (Neumann 2008).
The provision of maps via the Internet is a rapidly evolving area of development and investment. While classical cartographic concepts still apply in how geospatial information can best be presented, the interactive nature of the Internet has offered (and continues to offer) novel ways to capture and communicate geospatial information.
Web mapping is conceptually fairly straightforward, but the myriad techniques for actually implementing maps on the web can become quite detailed and technical, which reflects the actual complexity hidden underneath the deceptively simple interactions we have with web maps on a daily basis. Beyond the most simple maps, computer programming skills are needed to develop and support web maps, with the most complex maps requiring teams of programmers and designers, each with specialized skills and duties.
Nevertheless, having some general understanding of how web maps are implemented is vital to anyone working with geospatial technology. This simplified introduction is provided with the caveat that since there are a large number of technologies that are evolving on a daily basis, this overview is outdated and incomplete. However, this page can be a starting point for further investigation of contemporary web mapping practices.
A computer network is a set of computers with electronic interconnections that allow them to communicate with each other.
The Internet a global network of computer networks that has become fundamentally important to contemporary communication, including the communication of geospatial data.
Devices on the Internet are uniquely identified by 32-bit internet protocol (IP) addresses. These addresses are commonly written as four digits (each representing one 8-bit byte) separated by periods. For example, this is the IP address of the web server for the University of Denver web site (http://du.edu):
The World Wide Web
The World Wide Web (WWW) is a vast, open repository of information resources located on web servers interconnected using the Internet. The web was proposed and initially developed by Tim Berners-Lee in 1989.
Servers are large computers or groups of computers that respond to clients.
Clients are devices like desktop computers, laptop computers and mobile phones.
Resources on the web are uniquely identified by Uniform Resource Locators (URLs). A Uniform Resource Locator has multiple parts. For example with:
- http: specifies the scheme for accessing the resource as Hypertext Transfer Protocol (HTTP)
- michaelminn.net is the domain name
- www. specifies a server within the michaelminn.net domain
- /geography/ is the path to the resource on the www.michaelminn.net server
This is the basic process of how an Internet client gets information from a server on the web:
- A person on a client types a URL or clicks on a link
- The domain name separated from URL
- Message sent to a domain name server which returns an IP address to the client (All the Internet knows is numeric IP addresses)
- Client sends request to IP address via a router
- Routers pass to higher level routers until find a router that knows the network that contains the IP address
- Request is routed to server
- The server responds to the request
- Response packet(s) make their way back to the client through the routers
- The packets of information are received by client, reassembled and provided to the client's application (such as a web browser) for use
- Repeat as necessary
At a more-detailed level, these are the different hardware and software components of that process:
The content in a web page is specified with three different languages:
- HTML (Hypertext Markup Language) specifies the content of web pages
- CSS (Cascading Style Sheets) specifies how that content is styled and presented
All three of these languages are rich areas for study, and if you are interested in learning more, a good place to start is to work through the free tutorials at the World Wide Web Consortium's (W3C) W3Schools.
Below is a simple example HTML file containing an IFRAME that brings a Google Map onto the page:
Types of Web Maps
The simplest form of map on the web is the Static Map where the map content is fixed and unchanging. These are images generated with GIS software or scanned from paper maps in order to tell a story.
Static maps can be dynamically-generated where the server runs software that generates a map image based on changing conditions or specific user requests. An example of this type of map are radar images from the National Weather Service that are based on radar data this is periodically updated and changes over time.
Of much greater contemporary interest is the Interactive Web Map, where users can interact with the map - zooming, panning and/or changing the types of data displayed on the map.
While rudimentary interactive maps were made available on the web starting in the early 1990s, a radical transformation occurred with the debut of Google Maps in 2005.
The use of tiles makes it possible to move around the map without having to load a completely new image - which would make such interaction impossibly slow and very taxing on both the browser client and the server.
Because you can zoom into and out of most web maps, the amount of area covered by a single tile varies. Accordingly, tiles must be made available at a number of different Zoom Levels. Zoom level zero covers the whole world at around 156,400 meters per pixel, while zoom level 19 covers around 1/4 meter per pixel.
Real-time and Animated Maps
For representation of highly dynamic data, animated real-time maps can be created. These require complex, custom programming.
How Do People Use Web Maps?
Wayfinding and Navigation: How do I get to a place?
Businesses and other organizations commonly use web maps to permit customers or patrons to find them. These can range from Google Maps with single placemarks to maps that interactively provide specific information on store, like addresses, hours and driving directions.
Search: What is nearby?
Web maps are commonly used to find businesses or services in your vacinity. This relates to a larger use of geospatial data called Location-Based Services, although that term is more-commonly associated with mobile applications than web maps.
Location Information: What are the characteristics of a location?
Users commonly need information from an organization or governmental entity on specific locations, and web maps are excellent ways of providing an interactive way of accessing that information. For example, the governments in many counties permit access to property parcel information via web maps, usually via ESRI software.
News: Where is something happening?
Static maps have long been used in print media to give geographic context and explain spatial relationships in news stories. This tradition has continued with the use of both static and dynamic web maps as part of a panoply of data visualizations used on news websites.
Collaboration and Advocacy: How can I help?
Data flow with most interactive maps is largely unidirectional. Users make requests to map servers, the data displayed comes from the mapping service and users do not directly make changes to that data.
Collaborative web mapping not only provides data to users, but allows users to modify and augment the data on the server. To some extent, Google Maps could be considered collaborative in that users can submit reviews of restaurants, although users cannot directly change Google data.
However, projects like OpenStreetMap are based on volunteered geographic information supplied by users and are truly collaborative.
Collaboration through web maps has been especially valuable for disaster relief in developing countries where commercial mapping providers often do not have a financial incentive to create commercial data. For example, below is a product from the Humanitarian OpenStreetMap Team aiding Red Cross work in the Philippines following Typhoon Haiyan in 2013.
Analysis: Why are things where they are?
Perhaps the most sophisticated level of web mapping provides the capability to do complex analysis of geospatial data. This begins to cross the line into cloud Software as a Service (SaaS) and web applications.
One such service is ArcGIS Online, which not only facilitates the creation of simple, embeddable web maps, but also provides tools for spatial analysis.
A somewhat more experimental approach is CyberGIS, a web interface into a supercomputing infrastructure that allows sharing and collaboration on data-intensive and computationally-intensive research projects.
Exploration and Amusement
Many people find wandering the web to be an enjoyable activity in and of itself, even if there is no specific objective to the exploration. Nathan Francis has a list of the Coolest Uses of the Google Maps API.
Who Creates Web Maps?
A number of different types of jobs are associated with the creation and dissemination of web maps:
- Marketing and eCommerce
- Web Developers
- Data Visualization Designers
- Cartographic Developer
- Software Engineers / Developers
- Server and Systems Administrators
- User Experience / User Interface (UX/UI) Designers
As with GIS in general, web mapping is another skill in the toolbox of a GIS professional, and that skill usually compliments other skills in facilitating communication of geospatial information.
The Technologies Behind Web Maps
All maps start with some kind of geospatial data, real or imagined. Vast amounts of geospatial data are constantly being generated by a variety of private and public entities. Governments, especially in the USA, are rich sources of freely-accessible geospatial data. Some notable governemntal sources include:
- The federal US Census Bureau makes much of its data available through its American FactFinder website. This data is usually made available by place names (states, cities, census tracts, etc) and must be joined with Tiger/Line geospatial boundary files to be used for mapping.
- The USGS makes a vast amount of current and historic satellite data available through its EarthExplorer website.
- Almost all cities maintain significant amounts of geospatial data, such as property boundaries, utility lines, crime, etc. Many cities make some portion of their data freely available to the public, both as interactive web maps and as downloadable data files. For example, the city of Spokane maintains the MapSpokane web mab as well a GIS data download page.
Geospatial data usually exists in files at some point in its lifecycle. Common geospatial data file formats used to store and upload data for web maps include:
- Shapefile: This format was developed by ESRI in the late 1990s. While the age of this format is reflected in its numerous limitations (such as column name length limit of 10 characters), this format is supported by a wide variety of GIS software and is still commonly use for sharing geospatial data on the web, usually in ZIP archives.
- KML: Google Earth/Maps exchanges geospatial data in the Keyhole Markup Language (KML) format. KML is designed for the web and contains information on how the geospatial data should be displayed on a web map (like Google Maps) or in Google Earth. Since KML was designed for simple web mapping, it is not particularly good for storing complex attribute data. Most GIS software can read KML files, but shapefiles are usually preferred for serious analysis or when working with data sets of any significant size. The Keyhole part of the name comes from the name of the software company that developed the language before being bought by Google in 2004, and that company was named after the KH series of Corona US intelligence satellites launched in the 1960s and 1970s.
- GeoTIFF: The Tagged Image File Format is a standard format for storing raster graphics image data that was originally developed by the Aldus Corporation (now Adobe) in 1986. Because GIS data can also be stored as raster data, the format can be used with extra geospatial referencing parameters as GeoTIFF files to store GIS raster data, such as satellite or aerial imagery.
- GPX: GPs eXchange format is an format for storing Global Positioning System (GPS) data using eXtensible Markup Language (XML). It is a format commonly used to download GPS waypoints, routes or tracks from GPS recorders.
- Spatialite: SQLite is a file format and associated software library that can be used to store and access data using Structured Query Language (SQL) without having to use a complicated SQL database server. SpatiLite is an extension of SQLite that can be used to store and share geospatial data in a single SQLite file.
- CSV: Comma Separated Variable files are simple text files that are used to store table data as lines of text with fields separated by commas. When all else fails, it is the simplest way of storing and sharing latitude/longitude point data.
Geospatial data must usually be edited and "cleaned up" before it can be used. Common tools include Micro$oft Excel and ESRI's ArcMap, although the open-source and freely-available desktop GIS software QGIS can be an attractive option if you do not have to work in an enterprise environment.
Map and Web Servers
Web data is accessed from Web Servers. Web servers run software that receives requests from web clients, accesses data from files and databases, and then returns that data. Common web server software includes:
- Apache (in Unix/Linux environments)
- Micro$oft's Internet Information Services (IIS) (primarily in corporate environments)
Individuals, organizations or companies that do not have the means or interest in buying and maintaining their own physical web servers will contract with Web Hosting companies to provide web servers. There are dozens of hosting companies large and small, but some well-regarded web hosting companies include:
Web hosting companies and internet-based companies like Google maintain massive Server Farms that can have thousands of servers and consume as much electricity as medium-sized towns.
For web mapping, a Map Server is additional software on the server that converts geospatial data into a format that can be visualized on a client.
- ArcGIS for Server provides robust map services, and is most suited to an enterprise environment
- MapServer is an established freely-available open-source map server software that can be used by non-ESRI organizations to publish geospatial data
- GeoServer is a newer Java-based open-source map server
Organizations with anything but the simplest web presence need a Software Framework for managing content.
- Large corporations commonly use Micro$oft's ASP.NET software framework that integrates with the other Micro$oft sofware they use to run their business and provides a stable technical environment for developing web content and web applications.
- Another common framework is Adobe's ColdFusion.
Languages commonly used for server-side development include:
- C# (for .NET)
Organizations also often rely on Content Management Systems (CMS) that run on their servers and work along with the core web server software. A CMS simplifies the process of maintaining web content among different developers and over time. Common open-source CMSs suitable for small and mid-sized organizations include:
Third-Party Web Services
Acquiring, maintaining, and serving the data used in an ordinary web map requires a significant amount of money and resources. Accordingly, most organizations rely on third parties that specialize in mapping services, especially for the tiles used as base maps in almost all web maps.
Google and Micro$oft's Bing both make their tiles available to web map developers for free. In the open-source world, OpenStreetMap provides tiles.
A number of companies also provide map services at a sliding fee scale depending on the amount of resources needed, and free for a limited amount of private development. These services also generally provide a web interface for developing maps that are intuitive for non-programmers and provide features to create attractive maps with a high level of visual design quality. Some of these services include:
Client-Side Languages and Software
Web maps are displayed in a web browser. The most common desktop browsers in terms of market share as of July 2016 include:
- Chrome (51%)
- Micro$oft Internet Exploder (30%)
- Firefox (8%)
- Safari (5%)
- Micro$oft Edge (5%)
- Leaflet.js: easy to use but with some limitations in capabilities
- OpenLayers: lots of features but very complex
For many organizations, information technology in general and GIS in particular is needed in support of the core mission rather than being the core mission itself. For example, a county assessors office is primarily concerned with keeping track of property valuations and taxes rather than innovative web mapping.
For such organizations, the easiest course of action is to use standard, integrated software platforms, like ArcGIS, which provide seamless interconnection between desktops, databases, mobile devices and web maps. This also permits an organization to rely on a community of trained professionals who can join the organization without an extensive learning curve. While such software is expensive, the Total Cost of Ownership is likely less than the expense and trouble of hiring developers to reinvent the wheel.
While there is a large and growing body of non-ESRI shops, if your career interest is working in enterprise GIS, you should gain a working familiarity with the ESRI suite of products.