Less Is More

摘要

The book Geographic Information Science and Systems, released in 2015, is a fully revamped version of fhe third edition published in 2011 but written by the same four authors, one from the US and three from the UK. The result is a solid volume which weighs no less than 1.1kg according to the dispatch note. The authors are each notable figures in the industry. Michael Goodchild is retired professor of geography at the University of California; Paul Longley is professor of Geographic Information Science at University College London; David Maguire is vice-chancellor at the University of Greenwich and formerly with Esri; and David Rhind was CEO of Ordnance Survey and serves as member of the Editorial Advisory Board of GIM International. The 19 chapters, distributed over nearly 500 pages, provide a vista on the latest advances in the rapidly evolving Gl science and the allied digital tools and techniques used to collect, store, process, analyse, visualise and distribute geodata and information. After the Introduction (Chapter 1) the book has been divided into four parts. These are (1) Principles; (2) Techniques; (3) Analysis; and (4) Policy, Management and Action. Each part consists of four or five chapters. The arraying of the broad spectrum of topics based on this ordering seems sound but has an inconvenient consequence; from time to time one does not find a topic where one would expect to find it. For example, GNSS is treated as GPS in the georeferencing chapter (Chapter 4) as a useful tool for measuring the 3D coordinates of ground control points. One would also expect a fully dressed coverage in Chapter 8, which deals with data collection, but here GNSS is absent. Some of the topics are scattered throughout the book, such as mobile GIS systems which are handhelds for capturing geodata in the field. These are covered in Chapter 6 (Gl system software) and in Chapter 10, which covers the Geoweb. The same is true for virtual globes, including Google Earth and Microsoft's Bing Maps. They are branded as GIS software but the topic is also touched upon in Chapter 10 (geoweb) while one would expect to come across the topic - first and foremost - in Chapter 12, which is on geovisualisation. Chapter 4 is insightful as it not only touches upon metric reference systems, which are essential to the making of maps, but also upon postal codes, IP addresses and cadastral parcel numbers as useful sources for georeferencing manmade objects. The section on surveying in Chapter 8 only includes total stations by showing - for a large part - a photo of a surveyor and a total station mounted on a tripod at a road construction site. The authors state: "Two people are usually required to perform a survey, one to operate the total station and the other to hold a reflective prism". This account ignores the advances in robotic total stations in the last decade. Added to this, it is not clear why some data collection techniques are covered and others are left out. For example, a light is shone on airborne Lidar but ground-based laser scanners and mobile mappers, i.e. cars, vans, locos, boats and other vehicles equipped with laser scanners, digital cameras and positioning sensors remain absent. Data acquisition techniques are arranged based on whether they capture data in the form of rasters or vectors, with the odd outcome that airborne Lidar is touched upon in the vector data section. Of course Lidar acquires points, which is a vector feature as are lines and polygons, but the only physical meaning of these points is that they are samples lying on a curved surface, the envelope of an object or group of objects. Lidar points are blindly sampled and soon after collection they are usually transferred to raster format through interpolation, TINs or point clouds. What is the benefit of categorising data acquisition techniques in accordance with the way geodata is modelled in geographic information systems?