2/27/2019

Tutorial ArcGIS: Chow Data PART 2

2/27/2019

TUTORIAL ARC GIS GETTING TO KNOW ARCGIS DESKTOP

Chapter 3: Chow Data PART 2

Tutorial ArcGIS: Chow Data PART 2
Tutorial ArcGIS: Chow Data PART 2

The concept of layer

  • The layers link to a data source
  • A layer file (* .lyr)
  • Saves symbology, display scales (...) outside ArcMap document.
  • Can be created and viewed in ArcCatalog
In a map document, you display geographic information in the form of layers, each layer grouping a particular type of entity. The table of contents listing all the layers displayed in the map and shows the various features available in each layer.
Tick the box in the front name of each layer indicates that the features are visible.
You can change how each layer is drawn and adjust the display scale Using the Display tab of the Properties dialog box.


Data sets can be:

  • Vector datasets (layers of entities), blankets, shapefiles, file CAD, or ArcSDE geodatabases personal.
  • Raster datasets (raster layers), grids and images.
  • Games tabular data (INFO Tables, dBase files and RDBMS tables).
  • TIN Datasets
This way of reference data can always view the latest version of the data.

The .lyr files

Each layer can be recorded regardless of the map document. Layer files * .lyr contain all the properties of the layer name, symbology, display scales, reference to the data source. You can create multiple layers of files from a single data source.

The thumbnails

In ArcCatalog, each layer can be assigned a "thumbnail". 
You can create a thumbnail in zooming in on the area that best represents your data or zoom to the full extent of the theme. 
Good a thumbnail is generated automatically when you save the document, you can create manually.  Once created, the thumbnail becomes a reflection of your data at any time. 
When you change the source of your data, consider recreating the thumbnail.

layer  properties

Each layer has properties for specifying how entities are displayed, the symbols, labels, and attributes of the layer. To change the properties of a layer, you can double-click on this layer or call the context menu of the layer and run Properties.
The properties of one layer are organized in different tabs:
  •  General
  •  Source
  •  Display
  •  Symbology
  •  Fields
  •  Set of definition
  •  Labels
  •  Joins and Relates
The Symbology tab that interests us in this chapter is used to define the properties of symbols and classification of the legend of the layer.


symbology of layer

The standard symbology proposed by ArcMap ™ assigns the same icon to all entities of the layers
(Single symbol). ArcMap nevertheless allows building more advanced symbologies.
There is five large representation of families:

Entities:

This method displays all features in a layer with the same symbol.

Categories:

This type of representation is most often used to represent qualitative values. 
We distinguish three methods for this type of representation: representation by unique values, unique values multiple fields, and correspondence with the symbols of a style. 
These different methods are detailed a bit later in the chapter.

Quantities:

This type of representation is used to represent quantitative values. 
There are four methods for this type of representation: graduated colors per performance, the density of points, graduated symbols and proportional symbols. 
These various methods are described a little later in the chapter.

For diagrams:

This method allows representing several numeric attributes for each entity. 
The different values can be represented by means of a bar chart/columns, using a diagram sector, or by using a stacked graph. 
The field on which can apply this type of representation is necessarily digital.

Multiple attributes:

This type of symbology takes into account several attributes. 
You might, for example, want to symbolize the road network of a department using two attributes, type of road and traffic daily example. 
You would vary by the color of the line depending on the type of road and would be varying the thickness of each line based on the daily traffic.

Represent qualitative values

  • The layers are displayed using the values of a discontinuous field
  • Three methods: Unique values/Unique values over several fields/Correspondence with the symbols of a style
You can view all entities of the layer using the same symbol or display each entity with a different symbol.

Viewing layers using the values of a discontinuous field

Entities are displayed in functions of the various categories to which they belong, such as channel type, soil type, the name of the country ... In the example above, the French departments are
represented according to their home region.
There are three methods in ArcMap to represent entities according to qualitative data:

Unique values

Each entity is displayed with a unique symbol assigned based on values in a field of the table.

Unique values in several fields

Each entity is represented as a function of values in multiple fields of the table.

Correspondence with the symbols of a style

Each entity is represented using symbols stored in a style file.

Represent quantitative values

  • The layers are displayed according to values measurable
  • Four methods: Graduated colors/Density points/Graduate Symbols/Proportional Symbols

Quantitative maps can represent the entities depending on quantifiable data.
 He exists ArcMap four methods of representation of quantitative data.

Display data using quantitative values

The layers are displayed using numeric attributes.
 Each entity is represented by a symbol that can be easily compared with other symbols of the card. It is thus possible to quickly compare the values assigned to each entity for the same attribute.

Four methods

  • Graduated colors
A color gradient is used to represent quantity. Each entity of the layer is represented by a color which varies depending on the value of the attribute.
  • Dot density
This method of representing polygon features with a dot whose density is determined by the value of the field. 
The higher the value, the more the frame is dense. Each point of the frame corresponds to an absolute amount  (eg for a "population" field 100 inhabitants).
  • Graduated symbols
This method of representing entities by spreading in a number of classes calculated on the values of a field.
Each class is associated with a symbol size. 
Button Sort changes the number and the limits of each class.
  • Proportional symbols:
This method allows representing features with a symbol whose size is proportional to the field value.  If all the field values are different, then all the symbols have a size separate.
This method is like using an abacus.
The field on which can apply these 4 types of compulsory representation is digital.

Tutorial ArcGIS: Chow Data PART 3

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