The maps made using GIS software such as QGIS and ArcGIS are used for visualization purposes and consequently to make an informed decision based on the property being mapped. For instance, spatial data such as soil samples may be collected from the field, then mapped on a GIS software. The maps may show that certain areas have high content of a certain soil property such as Nitrogen and certain parts have low content of Potassium. This information is important for the farmers and other stakeholders in the agricultural sector in order for them to know which crops can do well in those areas or which fertilizers to add to the soil in order to boost the farm produce. This information is knowledge that will now make the relevant audience make a wise decision based on what is displayed on the map. After creating the maps therefore, a GIS professional should find a way of disseminating this information in order to reach the targeted audience as soon and fast as possible and in an effective way. The dissemination methods include: presenting the results in seminars, exhibitions, conferences, publishing the results in journals and most recently through web mapping.
Web mapping is therefore a way of disseminating spatial information/maps through the World Wide Web so that internet users can browse and find the relevant information with relative ease. Using the soil information example, frequent users of soil information can access the web mapping application, query and visualize the needed information in a dynamic manner as opposed to the static paper maps. Other areas where web mapping has been applied has been summarized in the Table 1.1
|Web map details||Web map URL|
|Homabay County Development Projects||http://www.homabayprojects.co.ke|
|County GIS portal||http://www.yavapai.us/gis/gis-mapping-applications|
|Real estate in Kenya||http://www.property24.co.ke/map-search|
|Crime Reporting and visualization||https://www.crimereports.com|
Just like building a house or any structure, web mapping also has a basic architecture that guides its development. Figure 1.1 summarizes this architecture
Figure 1.1, Source: https://www.e-education.psu.edu/geog585/node/684
A user of a web mapping application uses the browser which is the web client. Let’s say the application is displaying residential estates for sale and rent in Nairobi city and a way of filtering the desired house based on price, location, number of bathrooms etc. The client then request for a house that is in Buru Buru estate, has 3 bedrooms and the maximum price is Ksh 30000. After clicking on the search button, this information is sent to the web server via Hyper Text Transfer Protocol (HTTP). A web server is simply a computer system that processes the web client requests.
The web server acts by sending this information to the geospatial server which has the capabilities to draw maps based on the search criteria. The geospatial server fetches the request from the database that stores the spatial data. The database is queried based on the search parameters. The map is drawn and then passed to the web server which finally passes the map that contains the information that was requested to the browser of the client.
Before the data is taken to the database, they need to be prepared by the administrators. These applications are called the internal client applications e.g. QGIS and ARCGIS. The preparation may include: edits such as changing the coordinate reference system and digitization.
Web mapping has grown to be necessary in the field of geospatial engineering and I will be writing more detailed articles and manuals on the different components of web mapping. In this effect, I have divided web mapping into three different sections:
- Databases – I will be more biased towards the open-source databases such PostgreSQL/PostGIS.
- GIS server – Specifically I will write about GeoServer
- Client Side – OpenLayers and Leaflet will be covered.