Technology of generalization is used to transform the map of the source scale into a map of a smaller scale (destination scale).

Process of map transformation consists of a number of stages:

• formation of a nomenclature map sheet of destination scale;
• recoding of objects;
• support points generalisation;
• generalization of square hydrography objects;
• built-up area generalization;
• isolines generalization;
• generalisation of objects of small length or area;
• junction with adjacent sheets.

Formation of nomenclature map sheet of destination scale consists of the following processes:

• formation of the passport of nomenclature sheet;
• moving objects with dragging onto a frame;
• smoothing of topologically related objects;
• merge objects along junction lines.

1.1 Formation of the passport of nomenclature sheet

When performing the task of Uniting of map sheets for each four sheets of the digital topographic map of source scale, one sheet of the map of the corresponding source scale is automatically generated:

• for 4 sheets of scale 1: 25,000 - 1 sheet of scale 1: 50,000;
• for 4 sheets of scale 1: 50,000 - 1 sheet of scale 1: 100,000;
• or 4 sheets of scale 1: 100 000 - 1 sheet of scale 1: 200 000.

The selection of the map sheets of the source scale is performed automatically by the nomenclature of the map sheet of the destination scale. In this case, a sheet border and auxiliary lines (vertical and horizontal) are added into the map sheet of destination scale. Vertical lines run along the mating vertical sides of the frames of the map sheets of source scale. The horizontal line - along the mating horizontal sides of the frames of the map sheets of the source scale. The merge of objects, in the future, is performed along the auxiliary lines.

1.2 Moving objects with a dragging onto a frame

Moving objects from four sheets of a source map in a map of destination scale is carried out in full, except for frameworks of sheets of a source map. In this case, some points of objects that come out onto the frame have small discrepancies with the metric of the frame. The maximum divergences are shown by a red thickened line (see the Scheme of merged sheets of topographic maps). To avoid divergences when moving objects, the objects are automatically dragged to the frame of the derived sheet (a thin red line).

1.3 Smoothing of Topologically related objects

Automatic smoothing of the metric description of linear and polygon map objects with taking into account the available spatial topological links is performed in accordance with the specified smoothing accuracy (in millimeters on the map).

On the left figure there are shown the objects before execution of an automatic filtration, on the right - after execution. The marked zone contains topologically related objects.

1.4 Uniting of objects along lines of junction

Upon termination of carrying over of objects the uniting of objects along junction lines is carried out. During the process of uniting objects, there is carried out a search of corresponding pairs of objects along lines of a uniting, taking into account semantics. The semantics of the united objects are saved from both objects, except for the case when the objects being processed have conflicting semantics. In the absence of one of pair of objects, or at presence at objects of pair of conflicting semantics the uniting of objects is not carried out and an error message is output to the error log. The uniting of objects is carried out in accordance with the specified tolerance value for a uniting (in millimeters on a map).

1.5 Mathematical grid making

In the process of formation at first there is carried out an automatic removal of objects of a mathematical basis of the initial map, then - an automatic creation of objects of a mathematical basis (horizontal and vertical coordinate lines of the rectangular grid, points of crossing of coordinates grid, grid ticks of parallels and meridians, the central cross). The composition of the created objects of the mathematical basis depends on the scale of the formed map.

In the left figure there are shown the horizontal and vertical coordinate lines of a rectangular grid corresponding to a map of scale 1: 50 000, on the right - the coordinate lines of a rectangular grid received as a result of work of procedure of automatic creating a mathematical basis of a map of scale 1: 100 000.

2 Recoding of objects (classifier change)

Procedure of recoding is used to change the map classifier. In this case, there is carried out a customizing the tables of conformity of objects keys and codes of semantic characteristics of the classifier of the source map to the object keys and codes of the semantic characteristics of the classifier of the output map.

Formation of the passport of the nomenclature map sheet with the new classifier is performed automatically.

Carrying of objects of a source map to an output map is carried out by automatic change of type (localization) of objects according to breadboard models of conditions (tables of recode).

In the process there are used two classifiers and table of recode containing lists of conformity of keys of objects and codes of semantic characteristics of the classifier of the source map to keys of objects and codes of semantic characteristics of the classifier of an output map.

In the left figure, the white dotted line shows the territory of the marshes before automatic recode, on the right - the territory of the marshes have the appearance of shaded areas.

2.1 Support points generalisation

In order to ensure the preservation of state secrets at drawing up the maps of scale 1: 100 000 by maps of a larger scale, the coordinates of the points of planimetric base are rounded off (points of the state geodetic network, geodetic network of bridging, astronomical points, marks and reference points of the level net).

In the mode of automatic generalization of support points into the coordinates of points of the planimetric base, an accidental error is entered in accordance with the specified value of the spread and subsequent rounding with the established accuracy (in millimeters on the map).

2.2 Generalization of square hydrography objects

During the process of generalization, automatic replacement of parts of areal objects with a width less than the permissible one (in millimeters on the map), onto parts of linear objects is performed.

Areal objects are converted to linear objects in accordance with the table of recode. Processing of each areal object of hydrography consists of the following steps:

• search for linear objects (such as Inflows) adjacent to the processed areal object;
• replacement of parts of areal objects onto sections of linear objects;
• dragging objects such as Inflows to the metric of the received linear objects.

The left figure shows the areal river and linear inflows before the automatic replacement of the parts of the areal objects, on the right - after the completion of the procedure (the river has a linear view, the inflow is dragged to the new metric of the river).

2.3 Built-up area generalization

For the purpose of improvement of presentation of the image of quarters association of small quarters, and also increase in width passages is carried out. Processing of quarters is carried out in three stages:

In order to improve the visibility of the image of the quarters, small quarters are combined, and the width of the passages is increased. Processing of quarters is carried out in three stages:

• automated formation of passages;
• displacement of quarters, removal of unnecessary passages;
• automated formation of quarters.

At execution of the automated formation of passages in accordance with the specified width of passage(in millimeters on a map) between nearby quarters the temporary areal objects of type of Passages are created.

In the interactive mode, Move Object (Map Editor), the quarter shifts from the axial line of the adjacent passage if the visible parts of the quarters (not covered by the passages) have an area that is less than admissible. If there is no possibility of shifting the quarter (intersection with other quarters) in the interactive mode, Delete object (Map Editor) a deleting the passage is performed, which reduces the area of quarter.

At execution of the automated formation of quarters by the remaining after the interactive editing of passages, the cutting of quarters is performed.

In the Interactive mode, Merge Objects (Map Editor / Topology) there is carried out a merge of adjacent quarters, the distance between which is less than the specified tolerance (the width of the passage in millimeters on the map).

In the left figure the quarters of large settlement before execution of procedure of automatic formation of passages are shown, on an average - the expanded passages between quarters are marked by white color, on the right - quarters after performing the procedure of automatic cutting the quarters by the expanded passages are shown.

2.4 Isolines generalization

The generalization of the relief includes the generalization of isolines (contour lines, isobaths) and the generalization of point objects of the relief.

In the process of generalization, isolines (contour lines) are either deleted or converted to point objects with absolute height. Together with the deleted contour lines, the bergshtrihs and signatures belonging to them are also removed.

2.4.1 Processing contours

If the contour line is not closed, then the multiplicity of its height to the specified vertical interval of the output map is checked. If the contour's height is not multiple to the specified vertical interval, then the contour line is removed.

If the contour is closed, then it is checked whether it is a local extremum and whether it can be deleted. If the isoline is not a local extremum, then it is processed as non-closed (see above). If the contour is a local extremum, then its area is checked. If the area of the contour is larger than the threshold value, then the contour is not deleted. If the area of the contour is less than threshold value, then the contour (a local extremum) is deleted and instead of it a point object with absolute height is created.

The left figure shows the contours with a vertical interval of 10 meters before the automatic sampling of isolines is performed, on the right - the contour lines after the automatic sampling of isolines, taking into account the vertical interval of 20 meters.

2.4.2 Processing of bergshtrichs

Processing bergshtrichs is carried out after processing of contours. For each bergshtrich, the contour lines of the sheet on which the bergshtrich is located are viewed. If bergshtrich does not belong to any contour, then it is deleted. Belonging of bergshtrich to the contour is defined on coincidence (proximity) of the first point of the bergshtrich metrics and a current point of the contour's metrics.

2.4.3 Processing titles of contours

Processing titles of contours is carried out after processing of contours. For each title the contours of the sheet on which the title is located is scanned. If the title does not belong to a contour, then it is deleted. Belonging of title to the contour is defined by coincidence of value of absolute height from the text of the title and value of height of a contour, and also by proximity of the first point of the title metric and a current point of the metric of a contour.

2.5 Generalization of small objects

In the process of generalizing objects of small length or area, linear and areal map objects are processed. The degree of the length smallness is determined by the characteristic specified in the task parameters, the Minimum length (mm on map), degree of smallness of the areas - by the characteristic the Minimum square (sq.mm on map). At processing of objects the following processes are performed:

• uniting of linear non-closed objects of small length;
• uniting of areal objects of small area;
• replacement of type of linear and areal objects onto point objects.

The nearby linear non-closed objects of small length of one type and the areal objects of one type are united. Uniting of linear objects is performed when placed in the tolerance of proximity between the end points of the metrics (characteristic the Distance for line union (mm on map)). Uniting of area objects is performed when placed in the tolerance of proximity of the objects themselves (characteristic the Distance for area union (mm on map)).

Not united objects of small length or the area will be transformed to the point objects according to the table of recoding.

In the left figure the woods of the small area before execution of procedure of automatic sampling of small objects are marked, on the right - woods of small area are removed during the procedure work.

3 Coordination of adjacent sheets

The junction of nomenclature sheets of digital map implies the software-visual control and editing of the information on the objects going onto a frame for the purpose of definition of unambiguous, consistent characteristics of adjacent objects in accordance with the rules of the digital description.

After executing the application the Coordination of adjacent sheets (Tools/Run application) by using the vector map editor, a visual analysis of the processing results is performed. If there are error messages for the coordination, the causes that caused these messages are eliminated and the procedure execution is repeated.