Diagram Map Import

Nowadays the globalization process is stronger than ever and many companies sell products and services all over the world. That's why software applications in many areas need to provide geographical and mapping information to the end users. World's most popular format for storing such information is the ESRI shapefile. There are hundreds of freely available ESRI maps on the web and now you can easily take advantage of them using Nevron Diagram and its integrated mapping features. All you have to do is to put our diagramming component in your project and your mapping solution is just a few lines of code away.

Nevron Diagram for .NET Maps will enhance your .NET desktop or Web-based applications by adding intuitive, user-friendly and interactive Maps and geographical data, extending the Diagram to provide sophisticated graphs for your specific business needs.

The NMap class provides properties and methods that can help you adjust the appearance of any imported map. Let's take a look at them:

• Parallels, Meridians - you can use these properties to set the way the geographic grid is rendered. For each collection of arcs you can set the way they are rendered (below or above the other map objects, or not rendered at all) and whether to label them or not.
• Projection - allows you to specify the projection to use when importing the shapes (by default set to an Equirectangular projection). For more information about projections take a look at the Projections chapter.
• FillRules - a collection of the fill rules for the map. Fill rules are used in conjunction with data attribute values to automatically colorize maps. This approach is perfect for generating color thematic maps. For example, a map of the world could be colorized using available population data, or sales numbers for each country. For more information about fill rules take a look at the Fill Rules chapter.

The data binding feature of Nevron Map allows you to bind map features to the columns of a database table. For example, by calling the DataBind method of a shapefile, it will automatically acquire extra shape fields which are populated from a database table. These extra fields can then be utilized in the same manner as shape fields which have been imported from an ESRI shapefile. In order to perform the data biding you have to provide the following information:

• Data source - this can be a data table or a connection string (to an OleDb or a SQL Server database) and a table name.
• Primary key column - the name of the column from the attribute table of the shape file to use as a primary key. Note that the values in this column must uniquely identify the shapes in order for the data binding to work properly.
• Foreign key column - the name of the data table column to use for matching features with the data to import.
• Binding column - the name of the data table column we want to import data from. A matching between the value of the primary key column and the foreign key column is done and if they match the data in the binding column of the current record is added as a new attribute to the feature.

Fill rules are used to colorize a map based on the values of a shape field. When creating a fill rule you must specify the shapefile it is used on, the fill rule data column name and the colors to use (all of them or only the first, the last and their count). There are two types of fill rules:

• Value fill rules - all unique values in the fill rule’s data column are extracted and each unique value is colorized with the respective color. If the unique values are more than the colors, then the color counting is restarted and some different values will have the same color.
• Range fill rules - these fill rules are only applicable to data columns containing numbers. All unique values in the fill rule’s data column are extracted and then are grouped in a specified number of classes using the grouping algorithm specified to the DataGrouping property.

You can easily create and add fill rules to the FillRules collection of the map:

NMapFillRuleRange fillRule = new NMapFillRuleRange(countries, "POP_CNTRY", Color. White, Color.Black, 12);
fillRule.DataGrouping = DataGrouping.Optimal;
map.FillRules.Add(fillRule);

Following is an example of the different data grouping methods applied on a world map containing information for the population of each country:

Fig. 2 Fig. 2 - Map Equal Distribution data grouping. Equal Distribution - also known as quantiles, this method allows for unequally sized data intervals and involves adjustment of the interval limits until an equal number of data points can be slotted into each interval.

Fig. 3 Fig. 3 - Map Equal Interval data grouping. Equal Interval - also known as equal ranges (or steps), this method involves division of the entire data range into equally sized intervals.

Fig. 4 Fig. 4 - Map Optimal data grouping. Optimal - adjusts the size of data intervals in order to minimize the classification error and thus the map looks more balanced and the results seem more correct, with just a few shapes in the highest class as one would expect.

Simplification of a shape is a process which involves removing of points from the shape’s outline. The algorithm tries to preserve the original contour as much as possible. To control the level of data point reduction you specify a simplification factor - the greater the factor, the greater the reduction. The algorithm interprets the simplifica¬tion factor as follows: is p and q are 2 non adjacent points from the list and all points between p and q in the list are located at a distance smaller than the simplification factor from the line segment p-q then all points between p and q are removed. For example if points is a list of points, you can simplify it using only one line of code:

NPointFList simplified = NPointFList.Simplify(points, 3);



By reducing the number of points, the electronic size of the map is reduced, and this can lead to an improvement in map display performance and the storage capacity needed for saving the map.

All classes and interfaces referring to the mapping functionality are placed in the Nevron.Diagram.Gis namespace. Let’s take a closer look at them.

1. NEsriShapefile - represents an ESRI shapefile containing geographical data. Provide the name of the ESRI shapefile (.shp) to the constructor and then call the Read method. For each shapefile you can specify the name of the column it will use for naming the diagram elements and the min and max zooming factor it will be shown on.

2. NEsriMap - represents a collection of ESRI shapefiles. You can add one or more files using the Add method. It returns a reference to the ESRI shapefile, so that you can set one or more of its properties if you want to. The Read method is used to read all shapefiles in the map. You can use the indexer to get a reference to the shapefiles. The GetAllFeatures method returns all shapes in all shapefiles of the map. Using the Parallels and Merdians properties you can specify the way they are rendered. The Projection property determines the projection used to convert the 3D geographical data to 2D map data.

3. NGisFeature - this class is the base for all ESRI shapes. It contains two important values that are common for all ESRI shapes - the shape type (the possible shape types are described in the ENShapefileRecordType enum) and the attributes of the shaped. The attributes are read from the .dbf file that has the same name as the .shp file and are stored as a DataRow object.

4. INFeatureCreatedCallback - interface containing callbacks for shape creation. You should implement this interface if you want to be informed each time a diagram element is created and imported from the ESRI shapefile to the diagram. This makes it easy for you to apply additional styling on the imported diagram elements according to the attributes of each shape. For example if you want to make the cities that have population more than 5 000 000 two times bigger than the others you should use code similar to:

public void OnPointCreated(NDiagramElement element, NGisFeature feature)
{
NPointElement pe = (NPointElement)element;
float population = float.Parse(feature.Attributes["POPULATION"].ToString());
if (population > 5000000)
{
pe.Size = new NSizeF(2 * pe.Size.Width, 2 * pe.Size.Height);
}
}

5. NEsriImporter - this class is used to convert ESRI features to diagram elements and import them in your diagram. As said previously in the How to add a map section the class provides some properties that can help you control the importing process:

• PolygonsAsShapes, PolylinesAsShapes - determine whether to render the objects as shapes or as paths.
• ImportInMultipleLayers - determines whether to import the data from each ESRI file into separate layer.
• FeatureCreatedCallback - if you want to perform additional customization on each diagram element implement the INFeatureCreatedCallback interface and set it to this property.

6. NGisProjection - abstract base class for the projections that specify how to interpret the 3D map data as 2D rendering data. Currently the following projections are available:

Aitoff Map Projection Aitoff Map Projection Aitoff - Proposed by David A. Aitoff in 1889, it is the equatorial form of the azimuthal equidistant projection, but stretched into a 2:1 ellipse while halving the longitude from the central meridian.

Bonne Map Projection Bonne Map Projection Bonne - a pseudoconical equal-area map projection. All parallels are standard, with the same scale as the central meridian; parallels are concentric circles. No distortion along the reference parallel or the central meridian.

Cylindrical Equal-Area Map Projection Cylindrical Equal-Area Map Projection Cylindrical Equal-Area - represents a cylindrical equal-area projection of the Earth. The following is a summary of cylindrical equal-area projection's special cases: - Lambert - standard parallel of 0 degrees - Behrmann - standard parallel of 30 degrees - Tristan Edwards - standard parallel of 37.383 degrees - Peters - standard parallel of 44.138 degrees - Gall - standard parallel of 45 degrees - Balthasart - standard parallel of 50 degrees

Equirectangular Map Projection Equirectangular Map Projection Equirectangular - projection that maps meridians to equally spaced vertical straight lines, and parallels to equally spaced horizontal straight lines.

Eckert IV Map Projection Eckert IV Map Projection Eckert IV - pseudocylindrical and equal area projection. The central meridian is straight, the 180th meridians are semi-circles, other meridians are elliptical. Scale is true along the parallel at 40:30 North and South.

Eckert VI Map Projection Eckert VI Map Projection Eckert VI - pseudocylindrical and equal area projection. The central meridian and all parallels are at right angles, all other meridians are sinusoidal curves. Shape distortion increases at the poles. Scale is correct at standard parallels of 49:16 North and South.

Hammer Map Projection Hammer Map Projection Eckert VI - pseudocylindrical and equal area projection. The central meridian and all parallels are at right angles, all other meridians are sinusoidal curves. Shape distortion increases at the poles. Scale is correct at standard parallels of 49:16 North and South.

Kavrayskiy VII Map Projection Kavrayskiy VII Map Projection Kavrayskiy VII - a map projection invented by V. V. Kavrayskiy in 1939 for use as a general purpose pseudocylindrical projection. Like the Robinson projection, it is a compromise intended to produce good quality maps with low distortion overall. It scores well in that respect compared to other popular projections, such as the Winkel Tripel, despite straight, evenly-spaced parallels and a simple formulation. It has been used in the former Soviet Union but is almost unknown in the Western world.

Mercator Map Projection Mercator Map Projection Mercator - introduced in 1569 by Gerardus Mercator. It is often described as a cylindrical projection, but it must be derived mathematically. The meridians are equally spaced, parallel vertical lines, and the parallels of latitude are parallel, horizontal straight lines, spaced farther and farther apart as their distance from the Equator increases. This projection is widely used for navigation charts, because any straight line on a Mercator-projection map is a line of constant true bearing that enables a navigator to plot a straight-line course. It is less practical for world maps because the scale is distorted; areas farther away from the equator appear disproportionately large. On a Mercator projection, for example, the landmass of Greenland appears to be greater than that of the continent of South America; in actual area, Greenland is smaller than the Arabian Peninsula.

Miller Cylindrical Map Projection Miller Cylindrical Map Projection Miller Cylindrical - a modified Mercator projection, proposed by Osborn Maitland Miller (1897-1979) in 1942. The parallels of latitude are scaled by a factor of 0.8, projected according to Mercator, and then the result is divided by 0.8 to retain scale along the equator.

Mollweide Map Projection Mollweide Map Projection Mollweide - The Mollweide projection is a pseudocylindrical map projection generally used for global maps of the world (or sky). Also known as the Babinet projection, homolographic projection, or elliptical projection. As its more explicit name Mollweide equal area projection indicates, it sacrifices fidelity to angle and shape in favor of accurate depiction of area. It is used primarily where accurate representation of area takes precedence over shape, for instance small maps depicting global distributions.

Orthographic Map Projection Orthographic Map Projection Orthographic - a perspective (or azimuthal) projection, in which the sphere is projected onto a tangent plane. It depicts a hemisphere of the globe as it appears from outer space. The shapes and areas are distorted, particularly near the edges, but distances are preserved along parallels.

Robinson Map Projection Robinson Map Projection Robinson - made in 1988 to show the entire world at once. It was specifically created in an attempt to find the good compromise to the problem of readily showing the whole globe as a flat image. The projection is neither equal-area nor conformal, abandoning both for a compromise. The creator felt this produced a better overall view than could be achieved by adhering to either. The meridians curve gently, avoiding extremes, but thereby stretch the poles into long lines instead of leaving them as points. Hence distortion close to the poles is severe but quickly declines to moderate levels moving away from them. The straight parallels imply severe angular distortion at the high latitudes toward the outer edges of the map, a fault inherent in any pseudocylindrical projection.

Stereographic Map Projection Stereographic Map Projection Stereographic - it is a particular mapping (function) that projects a sphere onto a plane. The fact that no map from the sphere to the plane can accurately represent both angles (and thus shapes) and areas is the fundamental problem of cartography. In general, area-preserving map projections are preferred for statistical applications, because they behave well with respect to integration, while angle-preserving (conformal) map projections are preferred for navigation. The stereographic projection falls into the second category.

Van der Grinten Map Projection Van der Grinten Map Projection Van der Grinten - neither equal-area nor conformal projection. It projects the entire Earth into a circle, though the polar regions are subject to extreme distortion. The projection offers pleasant balance of shape and scale distortion. Boundary is a circle; all parallels and meridians are circular arcs (spacing of parallels is arbitrary). No distortion along the standard parallel at the equator.

Wagner VI Map Projection Wagner VI Map Projection Wagner VI - a pseudocylindrical whole Earth map projection. Like the Robinson projection, it is a compromise projection, not having any special attributes other than a pleasing, low distortion appearance.

Winkel Tripel Map Projection Winkel Tripel Map Projection Winkel Tripel - a modified azimuthal map projection proposed by Oswald Winkel in 1921. The projection is the arithmetic mean of the equirectangular projection and the Aitoff projection. Goldberg and Gott show that the Winkel Tripel is arguably the best overall whole-earth map projection known, producing very small distance errors, small combinations of ellipticity and area errors, and the smallest skewness of any map. In 1998, the Winkel Tripel projection replaced the Robinson projection as the standard projection for world maps made by the National Geographic Society.

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