The article addresses to a fundamental issue facing the concept of the Digital Earth in 2020 - what is the definition of the Digital Earth? 22 years after the announcement of the concept and 15 years after its first mass and successful implementation in the service Google Earth in 2005 this question remains unanswered. In the article the current status of the development of the Digital Earth concept by 2020 is considered, a methodology for the definition of the Digital Earth, based on the classification of the diversity of existing geospatial approaches and the identification of key factors that provide its unique functionality, is proposed and discussed. Distinction between the Digital Earth and others geospatial approaches is provided. The intrinsic connection of definition and classifications is grounded, the new definition of the Digital Earth and complimentary classification of geospatial methods are offered. Semiotics aspects of the Digital Earth are discussed briefly. The question of the eligibility of technologies and systems to the Digital Earth is considered. The perspective issues of further development of the Digital Earth are considered.
In 2020 the Digital Earth initiative, first introduced by U.S. Vice President Albert
Gore in 1998, turned 22 years old. Digital Earth was being promoted as a new,
revolutionary approach to handling geospatial information with fabulous functionality,
and as a core of the new smart response and effective governance policy that will
offer many benefits to all mankind. In his well-known speech [
The prediction appeared to be remarkable. The year 2005 was indeed a turning
point in the development of the Digital Earth and marked the beginning of the
"geospatial revolution" with the unveiling of Google Earth [
On the one hand, the geospatial revolution has become a fact of our life and had an
irreversible impact on all mankind. Now the Digital Earth is officially recognized
throughout the world and has already established itself as a best approach for working
with geospatially located data. Digital Earth has gained huge popularity and widely
implemented with remarkable results. Google Earth, the clearest example of the new
concept, was downloaded more than billion of times six years after its launch [
The development of ISDE received a new impetus in mid-2010s with the start of
major infrastructure projects directly inspired by the Digital Earth concept and
organized under the umbrella of ISDE. China, Australia [
On the eve of 2020, the Manual of Digital Earth [
In 2020 the implementation of Digital Earth has become a mandatory requirement for quality management. The coronavirus pandemic COVID-19 has shown the extreme need of humankind to ensure sustainable development and to implement the Digital Earth as a state-of-the-art decision making support environment due to its global extent and scale-less nature. The need for the Digital Earth as a highly effective tool to support global decision making has reached an unprecedented level.
On the other hand, scientific and technological progress between 2005 and 2020
has been far more modest than expected 22 years ago. There is a visible and growing
contradiction between, from one hand, the urgent need for the Digital Earth and
sustained technological advance – and, from another hand, small and controversial
scientific developments in this field. Google Earth still remains the best embodiment of the
Digital Earth concept 15 years after its launch, even though its functionality has been
severely limited and development has virtually ceased [
The lack of definition does not allow to separate the Digital Earth from the variety of its analogues in the current situation of rapid emergence of new geospatial products and solutions, which can be difficult to attribute to any particular class. Thus, the discussion of the current status and prospects of the concept rises the question: what is and what is not the Digital Earth? Where are the limits of the Digital Earth?
Obviously, the definition and classification issues are interdependent – definition provides classification, and vice versa. The resolution of these issues is particularly important now, since the term "Digital Earth" is often understood in a hardly acceptable broad sense. There is a clear tendency to consolidate under the umbrella of the Digital Earth everything related to geospatial information, including all components of the process of creation, storage and use of localized data – remote sensing satellites, communications and navigation, data storages and transmission lines, hardware complexes and algorithms, mobile applications, etc. This approach, however, excludes discussion of the obvious novelty of the Digital Earth, because all information systems are now digital and all information is localized in geospace; it appears that there is nothing outside the Digital Earth that is obviously wrong. It is therefore important to undertake a comparative analysis, to identify and compare approaches and methods that are obviously not relevant to the Digital Earth.
Discussing the challenges in the development of the concept of the Digital Earth is
particularly important in the context of 2020. Beginning with the second decade of the
21st century, ISDE began to formulate a scientific agenda for the coming decade. The
first declaration Google Earth Vision 2020 was developed in 2011 [
Many attempts have been made to define the Digital Earth, but Gore's very first
definition of the Digital Earth still appears to be the most successful and effective. He
defined the Digital Earth as “...a multi-resolution, three-dimensional representation of
the planet, into which we can embed vast quantities of geo-referenced data” [
From the point of view of the common user perception, the answer to the question
"what is the Digital Earth" is quite simple – it's a generic term for a variety of
products similar to Google Earth. From a historical point of view, this issue also hardly
raises the questions - this is exactly the kind of clearly recognizable product was
anticipated in literature many decades before our era. The most striking example is,
probably, the magical "Woland's Globe" from Mikhail Bulgakov's novel "The Master
and Margarita" [
Understanding what is the Digital Earth equals to understanding what is not the Digital Earth. In turn, separation of these too classes produces the classification of whole variety of the similar approaches within their specific domain and to identify the relationships between them. To answer this question, it is necessary to define the domain within which the problem should be solved, and identify its counterparts. We can assume that this domain is geospatial visualization, because the perception of space should be visual and, accordingly, can only be provided by means of visualization. Within this domain, there are a variety of approaches to the representation of data - maps, globes, atlases, GIS, 3D-models, as well as new approaches that have appeared and developed practically simultaneously with Google Earth, but significantly different from it.
Albert Gore's definition revealed two key properties of the Digital Earth that can be used to classify the variety of geospatial products: 1) multi-resolution representation, and 2) three-dimensional representation. In fact, all geographic maps are confined inevitably to a certain scale and projection. Both these confinements are fundamental and determined by the basic cartographic principle. Throughout history, humankind has dealt only with geographic information confined to a strictly defined scale and making sense only at that scale. At the same time, this restriction was perceived as temporary and forced consequence of technical imperfection. Its overcoming in the future was envisioned, expected and perceived as achievement of the magic horizon of geography development.
Now this future has become a reality. The Digital Earth is not confined to just one scale and one projection. For example, in Google Earth the user can change smoothly and interactively both the view angle of the planet as a whole or the selected scene, and the distance to it by means of an extremely simple and natural interface. The existence of two polar geographic products - maps (confined to projection and scale) and the Digital Earth (free of these limitations) - makes it possible to use the degree of freedom in terms of scale and viewing angle as classification criteria to systematize the whole variety of geographic products.
A simple confinement-based analysis unveils four possible types of basic global
geospatial visualizations to be identified (Fig. 1): 1) maps and GIS (regardless of the
What is and What is not the Digital Earth? 5
type of their media) that incorporate the cartographic principle and confined to
specific scale and specific projection; 2) globes that allow viewing the scene from any
perspective from the upper hemisphere, but do not allow changing the scale; 3) atlases
and geoportals (cartographic-based solutions that allow selecting the required scale
from a discrete set, but do not allow changing the projection); and 4) Digital Earth,
completely free from restrictions of any kind in user's choice of projection or scale.
The visible representation of the features of these four types can be obtained with the
help of "Angle-Distance" diagrams [
To create a definition of the Digital Earth in accordance with these rules let's consider
the basic definition proposed by Gore in 1998 [
The striking properties of the Digital Earth look quite obvious and natural,
because they mimic the properties of the Earth itself as it percepted by human. This
What is and What is not the Digital Earth? 7
summa of properties was forecasted far before nowadays as a miracle geographical
system of the future [
Albert Gore directly emphasized in his speech that the important or even main
feature of the Digital Earth is the use of images instead of presenting information with
the help of signs: "We have long known that we have trouble remembering more than
seven pieces of data in our short-term memory. That's a low bit rate. On the other
hand, we can absorb billions of bits of information instantly if they are arrayed in a
recognizable pattern within which each bit gains meaning in relation to all the others"
[
Therefore, we could propose the modified version of the definition of the Digital Earth: Definition 1. Digital Earth is a scale-less and projection-less geospatial visualization of geocentric volume that similar to a real one by the means of incorporating the signless representation of the geospatial context.
The proposed definition is largely empirical because it combines the theoretical prediction of the Digital Earth with the experience of the usage of the applications inspired by this concept. As a result, this definition allows a critical discussion about possibilities of the Digital Earth, its relationships with different approaches to geovisualization, and contains significant potential for further interdisciplinary research. Moreover, this definition includes the vision of the typology of the geospatial visualizations, therefore it makes possible comparative study of the different approaches for geospatial visualization.
Use of images instead of cartographic signs to represent the geospatial context is a significant challenge to classical semiotics, which assumes that all information media must be treated exclusively as signs. Under this approach, all images, such as iconic images, are supposed to be classified as the most primitive so-called "iconic signs", while the Digital Earth is to be interpreted as a return from complex and “mature” signs to more primitive signs.
An alternative point of view indicates that attributing all images, including those obtained by remote sensing means, to iconic signs generates at least two logical fallacies.
1. It leads to violation of “law of parsimony”. 2. It contradicts the idea of artificial nature of signs and, therefore, their historical development.
In order to resolve a crisis, it must be assumed that information could be
transmitted not only by signs but also by other entities that were not signs. It had been
suggested that they should be called "zero signs" [
In this case, the Digital Earth should be considered a heterogeneous information system that uses both unsigned media and usual signs to achieve effective perception of the environment. The "zero sign hypothesis" needs to be critically considered, and the concept of the Digital Earth itself needs to be studied from a semiotic perspective.
Above considerations allow to separate Digital Earth and its alternatives. 3
The use of degrees of spatial freedom for classification of geospatial visualizations allows to reveal four definite types which fit the internal logic of the historical development of the geospatial method. All three alternative modes of geospatial visualization: 1) maps, atlases and GIS, 2) geoportals, 3) globes can be fully incorporated into the Digital Earth; otherwise is impossible. A factor that provides a new quality of perception in the Digital Earth mode is the use of images instead of signs as the primary carriers of geospatial context. Any of the four types of geo- visualizations allows to integrate the vast amount of information due to using of hypertext addressing mechanism, however the quality of its perception will be different. Digital Earth, due to its rich spatial context is possible to ensure the unrestricted perception of any spatial information in an extremely wide and not limited range of scales and in all possible diversity of directions of sight.
All geospatial approaches need raw information and the means to obtain it. All these methods are non-specific and can be used equally (with varying efficiencies) in any of the geospatial approaches. Therefore, data acquisition tools and related systems (geodesy and navigation, remote sensing, crowdsourcing, data processing capabilities, interfaces, etc.) are not the inherent components of the Digital Earth. Instead, Digital Earth will impact these variety of geospatial means and tools, significantly changing the ways for data capturing, processing and utilization. Also architecture and configuration of these systems will vary greatly accordingly with the requirements of new geospatial paradigm.
The same considerations apply to the analysis of the type of information media used in the Digital Earth and its analogues. The definition of "digital", which was a symbol of novelty back in the 1990s, has lost its original meaning by the second decade of the 21st century, since nowadays all information systems have completely or mainly migrated to the Internet ecosystem and are presented exclusively as computer ("digital") carriers. Nevertheless, the Digital Earth retains its exclusivity, and no other method of geo-visualization, also implemented through digital technologies, can match it in its capabilities. This transformation has not affected the essence of the information systems themselves – they were and still are based on the same signs as those developed centuries and millennia before the Internet. The revolutionary nature of the change is due to the fact that, for the first time in history, the Internet has enabled the free circulation of images constructed with the same "digital" signals as an usial text signs and digits, but simulating direct, non-signatory perception with increasing accuracy. The determinant of "Digital" in the name Digital Earth is historical – it would be more accurate to call it “Sign-less Earth” instead the “Digital Earth”. What is and What is not the Digital Earth? 9 The relationship between the Digital Earth, its counterparts and supplementary systems is shown in Figure 3. The Digital Earth is one of the four basic types of geospatial visualizations. All other types of geospatial visualizations - maps, atlases, globes - cannot be considered as the Digital Earth. Means of gathering geospatial information and other complementary systems like GNSS, remote sensing and communication satellites etc., cannot be attributed to the Digital Earth in the same way as well.
Digital Earth as a new approach to working with geospatial information is radically different from the other three, but uses the same sources of information – although its usage becomes completely different. For example, recreating a sign-less geospatial context requires a very different implementation of remote sensing orbital constellations. The architecture of control systems is changing, as the elimination of largescale image differentiation eliminates the only need for their hierarchical construction.
The Digital Earth no longer fits the paradigm of classic cartography. That is why understanding the nature of the Digital Earth, forming its scientific definition and internal development of the Digital Earth as an interdisciplinary scientific paradigm and relevant methods and technologies are so important.
Also should be noted some unresolved issues: 1.
Development of methods for visualization of solid media with a complex internal structure. This is necessary in order to extend the Digital Earth to represent areas that cannot be visualized by conventional means - the geology of Earth, processes in the atmosphere and outer space, etc. In fact interior of the Earth is the only "white spot" remaining in the modern Digital Earth.
To date, there is no Digital Earth standard that describes its minimum set of functions without regard to technical facilities and platforms, exchange formats, etc. The development of such a standard is extremely important to ensure the systemic development of the Digital Earth.
The Digital Earth was the first information system to use unsigned tools to represent geospatial context. The historical tradition, according to which signs were the only possible means of information transmission, and the development of increasingly complex sign systems, the most important means of social development, has reversed. The consequences of this turn for society have yet to be studied and understood.
Digital Earth is an unmatched tool for seamless consolidation of heterogeneous social information - for example, medical, biological, environmental, etc. The development and integration of effective tools for handling social geospatial information in the Digital Earth environment and the adaptation of management structures to this new tool for sustainable development is an urgent task.