[...]... a unit of interest, nor are they independent of scale 2 Accessing Existing Data Most GIS users will start using their systems by accessing data compiled either by the GIS vendor or by the organization for which they work Introductory tutorials tend to gloss over the amount of work involved even if the data does not have to be created from scratch Working with existing data starts with finding what’s... nothing because there is no information stored for anything in between the lines If the data is stored as areas (each plateau of equal elevation forming one area), then we could move around between any two lines and would always get the same elevation value Only once we cross a line would we ‘jump’ to the next higher or lower plateau Finally, the data could be 22 KEY CONCEPTS AND TECHNIQUES IN GIS. .. 2 KEY CONCEPTS AND TECHNIQUES IN GIS So what are the questions that a prospective GIS manager should look into before embarking on a GIS implementation? There is no definitive list, but the following questions will guide us through the remainder of this chapter • • • • • • • • • • What is the nature of the data that we want to work with? Is it quantitative or qualitative? Does it exist hidden in already... data one is working with is to collect all the primary data oneself and to have complete control over all aspects of acquisition and processing In the light of the costs involved in creating or accessing existing data this is not a realistic proposition for most readers GIS own their right of existence to their use in a larger spatial decision-making process By basing our decisions on GIS data and procedures,... data 6 KEY CONCEPTS AND TECHNIQUES IN GIS Figure 4 Geographic relationships change according to scale Originally, GIS and remote sensing data were truly complimentary by adding context to the respective other GIS data helped image analysts to classify otherwise ambiguous pixels, while imagery used as backdrop to highly specialized vector data provides orientation and situational setting Truly integrated... systematic introduction to the topic Many are self-trained and good at the very small aspect of GIS they are doing on an everyday basis, but they lack the bigger picture Others have learned GIS somewhat systematically in school but were trained with a particular piece of software in mind – and in any case were not made aware of modern methods and techniques This book also addresses decision-makers of all kinds... undocumented maps), we do not have the information that a GIS needs to match different datasets In that case, we have to resort to a process known as rubber sheeting, where we interactively try to link as many individually identifiable points in both datasets to gain enough information to perform a geometric transformation This assumes that we have one master dataset whose coordinates we trust and an unknown... vendor-specific features are lost during the data exchange process 12 KEY CONCEPTS AND TECHNIQUES IN GIS Figure 5 One geography but many different maps 2.2 Conversion Data conversion is the more common way of incorporating data into one’s GIS project It comprises three different aspects that make it less straightforward than one might assume Although there are literally hundreds of GIS vendors, each with their... areas, where the curvature could be neglected, the need to combine data from different sources, especially satellite imagery – requires matching coordinates from different 14 KEY CONCEPTS AND TECHNIQUES IN GIS Metadata Identification Information Citation Description Time Period of Content Status Spatial Reference Horizontal Coordinate System Definition: planar Map Projection: Lambert conformal conic Standard... often discouraging This author, for instance, searched in vain for imagery that helps to discern the vanishing rate of Irish bogs because for many years there happened to be no coincidence between cloudless days and a satellite over these areas on a clear day On the upside, once one has the kind of remotely sensed data that the GIS practitioner is looking for and some expertise in manipulating it (see . KEY CONCEPTS & TECHNIQUES IN GIS Albrecht-3572-Prelims.qxd 7/13/2007 4:13 PM Page i Albrecht-3572-Prelims.qxd 7/13/2007 4:13 PM Page ii JOCHEN ALBRECHT KEY CONCEPTS & TECHNIQUES IN GIS Albrecht-3572-Prelims.qxd. (pbk) Typeset by C&M Digitals (P) Ltd, Chennai, India Printed and bound in Great Britain by TJ International Ltd Printed on paper from sustainable resources Albrecht-3572-Prelims.qxd 7/13/2007. software in mind – and in any case were not made aware of modern methods and techniques. This book also addresses decision-makers of all kinds – those who need to decide whether they should invest in