3.5 XML

XML  is a means of describing data. It is a method of encoding data in text which renders the data easy to store, transport and interpret. It is not a language but provides a framework that allows users to write their own Mark-up languages for their own specific needs. GML is such a language which is concerned with the description of geographic content. It describes data or objects that have a spatial element by encoding geometry and spatial reference systems. The fact that it is based on XML means that it can be read and edited using any text editor, is easy to transport and transform and, crucially, can be easily integrated with non-spatial data.

This final point is incredibly important. For many years spatial data has been stored, viewed and analysed separately from non-spatial data. In recent years GIS developers have striven to integrate spatial data and analysis. GML enables the integration of geographical information by using a set of rules and guidelines (XML) which can be applied to any data type for any purpose. This means that geographic information can be integrated with a massive range of non-geographic data types thus, greatly enhancing the value and accessibility of spatial information.

The Ordnance Survey’s MasterMap dataset is a digital database of vector information describing geographical features on the ground in incredible detail. Individual building outlines, bollards, trees and road networks all have their own unique identifier called a TOID (Topographic Identifier) as well as information on their geometry and attributes. MasterMap is based on GML. The OS use GML because it's “well defined geometric primitives coupled with a structured mechanism for defining features ensures that when spatial data is exchanged in GML it can be interpreted and understood by everyone.”

Below is a sample of MasterMap for my house viewed in a GIS, and its associated GML.

MasterMap Data Around My House

Crown Copyright/ Database right 2009
An Ordnance Survey/ Edina supplied service

A Sample of the GML for the above MasterMap Data

3.4 Images and Graphics

Table Showing Main Differences Between GIF, JPEG and PNG Image Formats

	PNG	JPG	GIF
Format	24-Bit	24-Bit	8-bit
Colours	16 Million	16 Million	256
Compression	Lossless	Lossy	Lossless
Best For	Multiple Edits	Photographs	Simple Images

GIF (Graphics Interchange Format) is an image format developed by CompuServe in 1987. Its method of indexing using a colour lookup table and specifying the value of each raster cell as a position within the table makes it particularly suitable for images containing large areas of limited colours, as repetitions of sequences of bytes can be referenced according to their previous occurrence thus saving space. GIF is not a suitable format for complex images such as photographs. Complex images with smooth variations in colour and tone such as these are best suited to the JPEG file format, such named as it was developed by the Joint Photographic Experts Group. The 24 bit format allows for over 16 million colours. However, the compression does sacrifice some of the original data making it unsuitable for important images or those which will undergo multiple edits. The PNG (Portable Network Graphics) format seeks to combine the benefits of the jpg format with the compression rates of GIF by using a 24-bit format and the indexed colour method of storage. Because this format is lossless it is particularly suited to images which need to be preserved in their entirity.

GIS makes use of all three of these image formats both in bringing images into GIS for spatial enrichment (georeferencing) and exporting map documents for printing or use in other applications such as Microsoft PowerPoint. In addition GIS systems make use of other image formats such as BIL, IMG and JPEG 2000.

Below is the same map layout in JPEG, GIF and PNG image formats. All files are 99KB in size. As you can see, the JPEG has not coped well with the resizing.
                                                                             JPEG

GIF

                                                                             PNG

3.3 Internet/ WWW

The Internet and the World Wide Web are not the same thing. If the Internet were a road the www would be a bus. But if the Internet was the bus the passengers would be the www. And if the Internet were the passengers the www would be...don’t know. But you get the point.

The Internet is a networking infrastructure connecting millions of computers and allowing them to communicate with each other as long as they are connected to the Internet (or on the bus?). Information is shared between computers on the Internet via a variety of different protocols. The WWW consists of Web Pages constructed using the hypertext markup language protocol which are hosted on servers. The server-client architecture allows the server machines to respond to requests from clients and return the requested HTML documents via the Internet which are interpreted by the client Internet browser as web pages. Internet protocol numbers uniquely identify every computer in the world and are translated into more familiar domain names by the Domain Name System. These are combined with information on the local path of a document to form a Uniform Resource Locator (URL), which allows the server to locate and return the requested page to the client.

The Internet was developed in the 1960s by the American military to create a communications network impervious to nuclear attack. The World Wide Web came in the 1990s, initially as a means to share academic papers across the Internet.

It is easy to become swept up in the hype about the Internet and World Wide Web, however, it is important to consider the socio-economic bias. The digital revolution has occurred predominantly in the western, developed world and a clear digital divide exists.

Here, here and here are the web pages I created in this weeks practical.

3.2 Text/ Html

Different data formats use different binary encodings as an agreed method of interpreting sequences of binary numbers. For example, the American National Standards Institute (ANSI) developed an encoding for alphanumeric characters known as the American Standard Code for Information Interchange or ASCII. ASCII can be used to translate between seven digit binary sequences and alphanumeric characters. It is a format which is familiar to me in my profession as a GIS analyst via the ESRI ASCII Raster format which we use to store digital elevation models.


Different data formats allow computers to use binary code to represent data in different ways to support a range of uses and activities. For example, in GIS the .shp file format is used to store spatial information relating to a vector data type and .prj is used to store information about the geographic projection system. Most data types are proprietary so knowing which program should be used to view a particular data type is key. If I open an ESRI .shp file in Microsoft word, for example, the result is useless (see image). Different data formats require a particular program to allow the file to be read correctly and so enable the user to extract meaning from it.


So data formats allow us to extract meaning from different types of data by interpreting sequences of binary in different ways. Metadata and markup allow us to impart even more meaning to data essentially by providing data about data. For example, in a word (.doc) document, metadata might be used to denote the font type, size and colour. In GIS metadata is normally stored and displayed as an xml file. It is described in an Esri Whitepaper as "a summary document providing content, quality, type, creation and spatial information about a dataset".

3.1 - Introduction

Being completely new to blogs I was more than a little daunted about using this particular web 2.0 technology to document my understanding of digital technologies and architectures. However, having selected Blogger.com I have been pleasantly surprised.

Blogger.com is owned by Google, which is immediately evident in the style and ease of use of the website. Before setting up your blog users are invited to 'take a quick tour' which provides you with a brief definition and history of blogs. I particularly liked their view of blogs as a revolutionary tool which has altered not only the virtual world but "impacted politics, shaken up journalism and allowed millions of people to have a voice and connect with others". A bit of hyperbolising by Blogger.com? We shall see. What I was surprised to find was the prevalence of Business blogs within my own organisation, Aviva, for the dissemination of information on the business as a whole or particular projects. The most noteworthy is John Kitson's, our Sales and Marketing Director's blog . It seems the whole world's been blogging except me...

The service is organised in such a way as to make it appealing and accessible to non-technical users with options allowing you to customise the look and feel of your page such as altering the layout, colours and fonts without having to use Html. On signing in you are taken to your profile page which has clear links to allow you to view other peoples blogs via the 'Blogs I'm Following' and 'Blogs of note' tabs making the development of social networks a seamless element of the blogging experience. The options to share and present information also seem to be straightforward with buttons to add images or videos, edit Html and personalise your text.