CaGIS Vol. 29, Number 4

Testing the Usability of Interactive Maps in CommonGIS

Natalia Andrienko, Gennady Andrienko, Hans Voss, Fatima Bernardo, Joana Hipolito, and Ursula Kretchmer

The paper reports on an experimental study aimed at assessing the usability of five different interactive tools for exploratory analysis of geographically referenced data implemented in CommonGIS. Usability was assessed in terms of tool learnability, memorability, and user satisfaction. The study provided valuable data concerning the usability of each individual tool; we also derived some conclusions relevant to geovisualization techniques in general. We found that users were, in principle, able to understand and adopt the new ideas of map interactivity and manipulability. However, these ideas needed to be appropriately introduced; people could hardly grasp them just from the appearance of the maps and controls. An introductory demonstration was sufficient to understand the purposes of the interactive tools, and a short training session enabled people to use them. The importance of educating users is a particular challenge for geovisualization tools that are intended to be accessed over the Internet.

Keywords: Geographical visualization, interactive maps, usability engineering, usability evaluation, user studies.

Flexible Standardization: Making Interoperability Accessible to Agencies with Limited Resources

Nadine Schuurman

Semantic standardization is an integral part of sharing data for GIS and spatial analysis. It is part of a broader rubric of interoperability or the ability to share geographic information across multiple platforms and contexts. GIScience researchers have made considerable progress towards understanding and addressing the multiple challenges involved in achieving interoperability. For local government agencies interested in sharing spatial data, however, current interoperability approaches based on object-oriented data models represent idealistic solutions to problems of semantic heterogeneity that often exceed the level of sophistication and funding available. They are waiting for the market to decide how interoperability should be resolved. In order to assist in this transition, this paper presents a rule-based Visual Basic application to standardize the semantics of simple spatial entities using several classification systems. We use the example of well-log data, and argue that this approach enables agencies to share and structure data effectively in an interim period during which market and research standards for semantic interoperability are being determined. It contributes to a geospatial data infrastructure, while allowing agencies to share spatial data in a manner consistent with their level of expertise and existing data structures.

Keywords: Standardization, interoperability, semantic heterogeneity, classification, Visual Basic

A New World Geographic Reference System

Keith C. Clarke, Peter H. Dana, and Jordan T. Hastings

A new global georeferencing system —- the World Geographic Reference System (WGRS) -— is proposed. This system has particular advantages for location description and communication with electronic devices, i.e., in digital environments that are shared between humans and machines. The new World Geographic Reference System strikes a compromise between the dominant use of numbers in established scientific coordinate systems, such as latitude/longitude, and the colloquial preference for names, particularly names of administrative units and populated places, in everyday life. Specifically, WGRS defines a system of uniform regional grids, each 100x100 km in extent, anchored on and named by prominent cultural and/or physical features. Subsets of these regional grids, called local grids, which are particularly adapted to smaller places, also may be defined. A location within a regional or local grid is georeferenced by suffixing the grid identifier with a coordinate string of dotted-digit-pairs that represent interleaved Cartesian x-y displacements from the grid origin. A typical WGRS locator, for example, is US.DC.WAS.54.18.28, representing a 100x100 m area, the southwest corner of which is 0.512 of the way across (east) and 0.488 of the way up (north) in the Washington, D.C., grid, roughly the lawn surrounding the Washington Monument. This locator, which is easily interpreted by both humans and machines, also may be effectively communicated between them via computer networks using a notation, such as “wgrp://US.DC.WAS.54.18.28” in web code. The similarity of WGRS locators (WGLs) to Uniform Resource Locators (URLs) on the Internet is intentional, facilitating their use in Web and wireless application interfaces, especially those employed in location-based service systems.

Keywords: Coordinate systems, geocoding, georeferencing, mapping grids

Spatial Forecasting of Disease Risk and Uncertainty

Lee De Cola

Because maps typically represent the value of a single variable over 2-dimensional space, cartographers must simplify the display of multiscale complexity, temporal dynamics, and underlying uncertainty. A choropleth disease risk map based on data for polygonal regions might depict incidence (cases per 100,000 people) within each polygon for a year but ignore the uncertainty that results from finer-scale variation, generalization, misreporting, small numbers, and future unknowns. In response to such limitations, this paper reports on the bivariate mapping of data “quantity” and “quality” of Lyme disease forecasts for states of the United States. Historical state data for 1990-2000 are used in an autoregressive model to forecast 2001-2010 disease incidence and a probability index of confidence, each of which is then kriged to provide two spatial grids representing continuous values over the nation. A single bivariate map is produced from the combination of the incidence grid (using a blue-to-red hue spectrum), and a probabilistic confidence grid (used to control the saturation of the hue at each grid cell). The resultant maps are easily interpretable, and the approach may be applied to such problems as detecting unusual disease occurrences, visualizing past and future incidence, and assembling a consistent regional disease atlas showing patterns of forecasted risks in light of probabilistic confidence.

Keywords: Risk maps, kriging, choropleth maps, uncertainty, disease, forecasting, ARIMA

Variations of the Gringorten Square Equal-area Map Projection

1. Graham Cogley

Gringorten’s square equal-area map projection has been forgotten since its appearance in 1972. I describe a modern implementation, including details of how to arrange, in different ways, the fundamental Gringorten projection of a sexadecant (one sixteenth of the surface of the sphere) onto a triangle. The Gringorten Mark I projection is an arrangement in which one hemisphere forms a square, with the other hemisphere disposed around it so that the whole sphere projects as a diamond, which may then be rotated to appear as a square. I introduce an alternative arrangement, the Gringorten Mark II, which is twice as high as it is wide, with one hemisphere on top of the other. These variants are compared with some other square map projections. Maps that fill a rectangular space completely can be very useful where, as on computer screens, space is limited and must be used efficiently.

Keywords: Map projections, square maps, equal-area maps, computer cartography, optimization of computer screen space