18. Geographic information systems and technologies

18.1. The concept of geographic information systems

Geoinformatics is a field of knowledge that studies the methods and means of obtaining, storing, processing, transmitting and presenting space-time information associated with the geospace .

Geospace is the physical shell of the Earth with objects of natural and artificial origin located on it.

Spatio-temporal information is called geodata . They are divided into two groups:

- basic geodata (coordinate geodata)

- special thematic geodata (attribute geodata).

Geodata includes basic information about objects and phenomena existing in geospace, characterized by the presence of spatial connections between them.

Geographic information systems (GIS) are automated systems, the main functions of which are the collection, storage, integration, analysis of geodata and their graphic visualization in the form of maps or diagrams.

GIS originated in 1960–70. at the interface of information processing technologies in database management systems and visualization of graphic data in computer-aided design (CAD) systems, automated card production, network management. Intensive use of GIS began in the mid-90s. The twentieth century, when powerful and relatively cheap personal computers and more accessible and understandable software appeared.

Originally, GIS was a geographic information system. At present, GIS is integrated with automated systems for inventory, design, navigation, management, etc. Modern GIS are essentially information management systems, the functionality of which is much wider than geographic information systems.

Baseline data for creating a GIS:

- cartographic materials (topographic and general geographical maps, maps of administrative and territorial division, cadastral plans, etc.). Since the data obtained from the maps are georeferenced, they are used as the base layer of the GIS;

- remote sensing data (RSD) - materials of phototopographic surveys and other non-contact surveys, for example, hydroacoustic surveys of the seabed topography. The materials of such surveys provide both quantitative and qualitative information on various objects of the natural environment;

- the results of geodetic measurements on the ground, performed using geodetic instruments, satellite receivers, three-dimensional scanners, etc .;

- data from state statistical services for various sectors of the national economy, as well as data from stationary measuring observation posts (hydrological and meteorological data, information on environmental pollution, etc.);

- attribute data (temporal and descriptive information containing various information about objects of natural and artificial origin located on the physical surface of the Earth).

The location of GIS objects is determined by coordinate geodata, which contain metric information represented by a set of geometric elements: points, lines, contours and areas. The main form of representation of the coordinate data are digital models (CM).

For visualization of geodata in GIS, graphic models of coordinate data based on vector and raster models are used.

18.2. Classification of geographic information systems

GIS is developed and applied for solving scientific and applied problems of designing the infrastructure of territories, urban and regional planning, rational use of natural resources, monitoring of environmental situations, and also for taking operational measures in emergency situations, etc. Many problems arising in life have led to the creation of various GIS, which can be classified according to the following features.

The functional capabilities of GIS are divided into:

- for full-function general purpose;

- specialized GIS, focused on solving a specific problem in any subject area;

- Information and reference systems for home and information and reference use.

The functionality of GIS is also determined by the architectural principle of their construction:

- closed systems do not have expansion options, they are able to perform only the set of functions that are uniquely defined at the time of purchase;

- open systems are easy to adapt, expansion options, as they can be completed by the user with the help of a special apparatus (built-in programming languages).

By spatial (territorial) feature GIS are divided into:

- global (planetary) ;;

- nationwide;

- regional;

- local (including municipal).

By problem-thematic orientation:

- general geographic;

- environmental and nature management;

- sectoral (water resources, forest management, tourism, transport, etc.).

By way of organizing geographic data:

- vector;

- raster;

- vector-raster.

18.3. The main components of geographic information systems

The main components of the GIS include: technical (hardware) and software, information support.

Technical means is a set of hardware used in the operation of GIS. These include a workstation (personal computer), information input / output devices, data processing and storage devices, and telecommunications.

The workstation is used to control the operation of the GIS and perform data processing processes based on computational and logical operations. Modern GIS can quickly process huge amounts of information and visualize the results.

Data entry is implemented using various technical means and methods: directly from the keyboard, using a digitizer or a scanner, through external computer systems. Spatial data can be obtained from electronic geodetic instruments, using a digitizer or scanner, or using photogrammetric instruments.

Devices for processing and storing data are integrated in the computer system unit, which includes the central processor, RAM, storage devices (hard drives, portable magnetic and optical storage media, memory cards, flash drives, etc.). Data output devices - a monitor, plotter, plotter, printer, with the help of which a visual representation of the results of the processing of spatial-temporal data is provided.

Software - software (software) for the implementation of the functionality of GIS. It is divided into basic and applied software.

The basic software includes: operating systems (OS), software environments, network software, database management systems, as well as modules for managing data input and output tools, a data visualization system, and modules for performing spatial analysis.

Application software includes software tools designed to solve specialized tasks in a particular subject area. They are implemented as separate modules (applications) and utilities (aids).

Software of any GIS must include two main parts - a graphic editor and a DBMS.

Information support - a set of arrays of information, coding systems and information classification. The feature of storing spatial data in GIS is their division into layers. The multi-layered organization of an electronic map, if there is a flexible layer management mechanism, allows you to combine and display a much larger amount of information than on a regular map.

18.4. Information processing in GIS

Information processing functions in GIS should provide:

- input and output information;
- management of graphic and thematic databases, i.e. creating databases, filling them, searching for information, sorting, editing and adding data, issuing information on requests and a number of other operations;
- visualization of information, i.e., a visual display on the monitor of information stored in digital form in graphic and thematic databases, information can be displayed on the screen either as a cartographic image or in the form of tables, graphs, diagrams, etc. p., showing the results of the performed data analysis;
- work with a cartographic image: moving it in an arbitrary direction, scaling; setting the elements of the image design (color, type of lines, etc.); control windows on the screen; image editing, etc .;
- a joint analysis of graphic and thematic information, which allows to identify links and patterns between objects and phenomena, the dynamics of the development of certain processes.

Information processing in GIS can be divided into three levels:

- at the level of information gathering - deciphering photographs and cartographic images, processing remote sensing data by digital photogrammetric systems (DPS) to obtain coordinate data, converting geodetic measurements into coordinate data, grouping attribute data according to classification features characterizing the properties of objects;

- at the level of modeling - editing of cartographic data, analysis of attribute data, formation of reporting forms at the request of users, etc .;

- at the level of data presentation - generalization of cartographic images - selection and display of cartographic objects according to the scale, content and thematic focus, performed through the procedures of classification and generalization of geodata.

With the help of GIS perform spatial modeling of objects and phenomena.

When modeling in GIS, the following types of data operations are distinguished:

- operations of converting formats and data representations;
- projection transformations;
- geometric data analysis;
- overlay operations;
- functional modeling operations.

Transformations of formats and representations are used as a means of exchanging data with other information systems, including GIS. Format conversion is carried out with the help of programs - converters.

Graphic data may have a raster or vector representation, with significant differences. Vector representation has significantly greater analytical capabilities than raster. The operation of converting a raster image to a vector (vectorization) is one of the main ones when processing graphic data in a GIS. The structure of any GIS includes a special vectorization program - a graphic editor.

To determine the position of objects in space, there are many coordinate systems (CS). To depict the surface of the earth on a plane, various mathematical models are used - cartographic projections. A group of mathematical procedures of GIS that transition from one coordinate system to another, the spatial coordinate system to a map projection, or the transition from one map projection to another is called projection transformations.

GIS software allows you to perform a series of geometric analysis operations. For vector models such operations are:

- determination of distances;
- determination of the lengths of the curves;
- determination of areas of figures;
- Transform points of the object.

A feature of the representation of geodata in GIS is the possibility of organizing them in the form of multiple layers. The essence of overlay operations is the imposition of opposite layers with the generation of derived objects and attribute inheritance.

GIS uses various analytical operations:

- calculation and construction of buffer zones;
- network analysis;
- generalization;
- digital modeling.

The development of automated methods for processing spatial information led to the emergence of a new direction in modeling - digital modeling (CM). The main objects of digital modeling are:

- digital elevation model (DEM);
- digital terrain model (DTM);
- digital object model (CMO).

The conversion of raw materials into digital vector form (digitization, or vectorization) is performed by two main methods:

- digitization on digitizer;
- scanning of the original analog materials, followed by digitizing on a raster substrate.

A digitizer is a digitizing device consisting of an electronic tablet and a pointer.

A paper map or a photograph to be digitized is strengthened on the tablet (the map is not allowed to be shifted during digitization). The pointer is a push-button device that moves around the tablet. The number of buttons on it depends on the type of digitizer and can vary from one to seventeen.

Working with a digitizer can be performed in two modes: discrete and continuous.

When working in the discrete mode, the operator manually traces the contours of the objects, combining the crosshair of the digitizer with the characteristic points of the digitized object and pressing the corresponding button at that moment, which leads to the transfer of the coordinates of points to the computer. Images of circled objects appear on the monitor screen.

When working in continuous mode, pressing the button is not required: the coordinates of points are recorded automatically, either with a constant step, or with a constant interval of stroke time. The disadvantage of this mode is the excessive number of points characterizing the position of the object, so it is preferable to work in discrete mode, although it requires pressing buttons.

The digitizer tablet has its own coordinate system, different from the coordinate system of the map, therefore a correspondence must be established between the two systems in order to transfer coordinates from one system to another: the digitizer must transfer the coordinates of the map to the computer. To recalculate the coordinates at the beginning of work, control points should be set, the coordinates of which are known in both systems of coordinates. The minimum number of such points is two, but a greater number of points improves the accuracy of digitization.

When digitizing map objects, it is recommended to adhere to certain rules, the observance of which allows you to communicate some additional information about the objects. For example, the fixed direction of the bypass of some linear objects: the river is circled from the source to the mouth.

Digitization on a raster substrate has a greater distribution, because it provides higher accuracy and performance.

Before digitizing the image is scanned. To maintain the necessary accuracy of cartographic images, the scanner resolution must be at least 600 dpi. The result of the scan is a raster file (GIF, TIF, PCX).

Opening this file in the GIS, get the image of the original cartographic material on the monitor screen. The first stage of processing the received image is its correction, which is performed, as in the case of working with the digitizer, by control points (points with known coordinates). After correction of the bitmap, it is started digitizing (vectoring - creating vector objects). Three technologies of digitization are applied: manual digitization, automatic and semi-automatic (interactive).

Manual digitization consists in tracing the contours of objects on the screen using the mouse with fixing (clicking the mouse button) the coordinates of the characteristic points of the contours.

Automatic digitization is performed using programs called vectorizers. The work of these programs consists in pattern recognition: they can identify and select from a raster individual point, linear and area objects, comparing the images with the patterns of conventional symbols embedded in these programs.

Semi-automatic, or interactive digitization is carried out using programs that automatically recognize objects on relatively simple raster images and turn to the operator for help when they cannot perform vectorization automatically.

The choice of a particular method depends on the complexity of the bitmap, the amount of work, etc. Fully automatic is possible only for relatively simple drawings. The complex parts of the image are vectorized manually, and for the remaining (simple) parts, an automatic or semi-automatic method is used.

In the process of vectorization by any method (both on the digitizer and on the raster substrate), many GIS functions are used to work with graphic objects: combining object nodes, checking line closures, finding discontinuities, deleting part of an object, connecting objects, transferring objects from layer to layer, and more. . P.

Most GISs allow you to perform spatial analysis, i.e. evaluate the relationships between objects by their spatial position. К числу наиболее распространенных функций пространственного анализа относятся функции проверки:

– лежит ли объект А полностью внутри объекта В;
– лежит ли объект А частично внутри объекта В;
– содержит ли объект А весь объект В;
– содержит ли объект А часть объекта В;
– пересекаются ли объекты А и В.

С использованием перечисленных функций производятся выборки объектов, попадающих в заданную область. Заданной областью может быть замкнутый контур, созданный разными способами. Широко распространенным в ГИС способом анализа пространственной близости объектов к какому-то заданному объекту (или к нескольким заданным) является создание так называемых буферных зон вокруг объектов, близость к которым анализируется.

A buffer zone is an area whose borders are at a certain distance from the object. For example, the buffer zone of a point object is a circle of a given radius, the center of which coincides with a point object.