Map and WebGIS
1.1. Map and WebGIS#
1.1.1. The role of maps#
Maps have played an important role in human activities for thousands of years. The world consists of things that have a geographic (i.e. spatial) relationship to each other, and while a map can be an exact replica of the world, it usually isn’t. Maps are models that contain representations of things in the world, but those models don’t need to be represented in a similar way to the things they represent, or even have the same spatial relationships. The real world is the domain of geographers and geographers, and the process of representing real world things on this plane is cartography. Geographers live on the surface of a large, approximately oblate ellipsoid, with topography, in three-dimensional space; maps are where cartographers live and work, and are small in scope and flat.
The Golden Age of Maps and Cartography corresponds to the Age of Exploration, when maps were the key to great wealth. The tools that propelled this golden age were compasses, sextants, and precise clocks. Digital maps, geographic information systems (GIS), and location-based services represent the next golden age of mapping and cartography. The tools driving this era are computers, the Internet, and the Global Positioning System (GPS).
In the modern world, clear and powerful messaging is essential for
business, science and political activity. All kinds of natural and human
events occur on the earth on which we live, generating trillions of
massive amounts of data every moment, and more than
80% of these
data are related to spatial locations. Whether the information to be
conveyed is demographic data, weather forecasts or environmental
monitoring data, it has a geographic distribution. Just as graphs
present numerical information in an easy-to-understand manner, maps can
show more clearly than any tabular format how information relates to
location, enabling users to view that information according to its
spatial orientation. While this distribution information is implicit in
the table of numbers, it is hard to see without showing it in a map.
Geographic information science transforms the data from the original two-dimensional character state into a spatial visualization language or knowledge that we can easily understand by studying the collection, storage, processing, analysis, expression and service methods of these data that are directly or indirectly related to geographic space. , so as to serve the environment, land, planning, water conservancy, energy, transportation, residents’ life and other aspects.
Historically, accurate maps have been difficult to make, and once maps are made, they are static and difficult to maintain and update. In the absence of other competing technologies, the very nature of these cartography limits the usefulness of paper maps. A decade ago, traffic route maps provided a good example of the limitations of paper maps. A lot of people keep them in their cars, even though they are always outdated. In order to present more information in a small page, fonts are often small, which makes them difficult to read. If you don’t want to see the streets, but rather see the locations of restaurants in town, you usually need to buy different types of maps. In other words, maps are often single-purpose files for a certain topic, acting as archives of past locations.
1.1.2. Application of Digital Map#
Digital maps ensure convenient and efficient presentation of graphic images. Therefore, they can also display current information dynamically and in real time. However, hard copy mapping work has been (and still is) the home page aspect of the collection and maintenance of underlying information. In fact, the dynamic nature of digital maps exacerbates maintenance efforts as performance and data requirements are very high.
The development of digital maps is driven by the needs of industry (eg mining), natural resource managers and researchers for geospatial information management. However, with the rise of the Internet and the commoditization of hardware, digital maps have become ubiquitous. Several digital map applications are now common, including weather maps displayed in morning weather reports, driving instructions obtained from GPS-enabled car navigation systems, and Internet sites that provide street maps on demand.
However, most of these applications cannot meet the needs of mobile users. For example, a GPS-enabled car navigation system can determine your current location and tell you how to get elsewhere, but since it only has access to onboard data (at best), it cannot provide services that require real-time information. These services will include optimal routing with congestion avoidance and real-time location-based services (eg, the lowest fuel prices within five miles).
However, applications are being developed that are network-aware and intelligent (ie, they are wireless and GPS-enabled). Some examples are management tools for GPS-enabled garbage collection, systems for providing driving instructions to emergency vehicles, and systems that allow shippers to locate goods in transit. Mobile technologies such as WiFi 2.5 and 3G cellular will bring new possibilities.
When wireless technology is ubiquitous and bandwidth is cheaper, what will be the killer application? Before the internet existed, no one would have predicted the popularity and profitability of a company like Google — a catalog of content from tens of millions of computers on the internet, free for anyone to use. This particular application was the invention of two college students who had a great idea and access to cheap technology. While I won’t try to predict what the killer mobile app will be, the fact that it will be a mobile app suggests that the map feature will be a necessary aid.
1.1.3. The role of open source GIS#
But the problem is that if some smart college student or entrepreneur wants to integrate killer apps and get rich, it can cost thousands of dollars to buy the data and/or services needed to break into the industry. Commercial proprietary technology, while powerful, is very expensive. Whether it’s outright purchasing of proprietary software, ordering spatial information, or outsourcing complete applications, producing high-quality map applications using commercial software is expensive. If there is a set of stable system requirements, some funds of the bank, and a market opportunity suitable for you, proprietary options may be a good choice.
However, if you are entering the market tentatively, with a dynamic set of system requirements (or none at all); or if you are short on funding, or just trying to use the technology, you should look into MapServer , which is the subject of this tutorial. MapServer is a map rendering engine that can be run in a web environment as a CGI script or as a standalone application through an API accessible from multiple programming languages. To quote the description from the MapServer home page, “MapServer is an OpenSource development environment for building spatially enabled Internet Web applications.” With help from the University of Minnesota, NASA, and the Minnesota Department of Natural Resources, MapServer is now hosted by nearly 20 developers from around the world.
There are many reasons why you may consider using MapServer: maybe your boss refuses to put the map into his pet project at the price of commercial products and tells you to find something on the Internet; Maybe you have a dataset containing some spatial information, and you want to share it graphically on the Internet; Maybe you want to expand your pet project. You think providing online maps will have a great impact; Or maybe you just like maps and think about making beautiful maps from digital sources that make you happy. But before you look at MapServer to see if it’s what you need, you have to understand what it’s not. MapServer is a tool for presenting geographic data to the web - it is not a fully functional GIS (although it can be used to build one).
1.1.4. Application of MapServer#
This tutorial introduces some open source GIS tools, but uses MapServer on the server side.
The following is a brief description of the three types of applications that can be developed using the MapServer API. (They can also be done via CGI, but the process is slow, cumbersome, and ugly.) By adding a MySQL database and a programming language like PHP, these applications can provide considerable functionality without a lot of development work, because This is difficult, the spatial awareness part is done by MapServer. None of these are particularly innovative, but they do demonstrate what can be done.
Real estate sales tools
By adding the latitude/longitude coordinates of each sale property to an MLS (multiple listing service) or similar service, you can create a spatially aware catalog that provides the functionality users expect from a graphical interface (such as click and drag space to pop up query and info boxes when the mouse hovers over a hotspot).
Real-time tracking and tracing
By collecting GPS locations in real-time and forwarding them back to the host over 2.5 and 3G cellular technologies, MapServer can help you build customer-facing applications that show the actual location of loads in real-time. MySQL databases are great for storing this type of data.
Real-time traffic consultation and congestion avoidance
Gather traffic levels electronically or by manually entering GPS coordinates, street addresses or intersections - MapServer can display traffic levels in real-time, served over the web, and suggest alternative routes.