Tutorial ArcGis Introduction PART 2

We have seen that the objects of the real world can be represented using dots, lines, or polygons. However, it is impossible to store individual entities in logical groups.
The Feature classes allow homogeneous entities together in a single unit.

Group objects into homogeneous units

In the example above the motorways, national and departmental can be grouped into one line feature class named "roads".
All customers of each franchise store can be grouped in a class of point features called "clients". The departments of the same region can be grouped in a polygon feature class named "Region."

Create classes of point, line, or polygon

You can create feature classes representing points, lines or polygons. A set of Data can sometimes support feature classes containing multipart entities.
For example, in a class of multi entities instead of representing each point as a single entity, an entity is consisting of a set of points.

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Metadata

The "data about data" (accuracy, description Data ...)

A powerful capability of GIS lies in the link between spatial data and data allottees.
Due to technical (formats ...) and legislative (intellectual property, distribution Public data) and the explosion of information, an organization of data poses Currently increasingly problems.
Metadata is data about data They quickly provide information.

Regarding any item stored in an information layer, such as:

•  The identification of the layer elements (name, date, keyword ...)
•  The quality of data
•  The spatial organization of the data (raster or vector) and geographic reference system.
•  Describing Objects and Attributes
•  The distribution of the data (contacts, formats ...)
•  The reference metadata (author ...)

Arc View provides all the tools to create, edit or view metadata.
These are stored with the data and are taken into account by all the administrative tools (copy, delete, Name change ...).

  

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Notion of scale

Large-scale maps/Small-scale maps/Define and display the scale

Notion of scale

The important concept and often misunderstood is that of the mapping map scale. In order to Represent a portion of the surface of the earth on a map, the surface should be reduced. 

Measurement This reduction is expressed by a ratio called "map scale". It is defined as the ratio of the distance from the card to the ground distance.

For example, if a road is 4.8 km by a line of 20 cm on this map, the formulations
the following could describe the scale of the map:
20 cm 4.8 km or 20 cm 480 000 cm or 1 cm: 24 000 cm or 1: 24,000

The second element is a representative fraction because of the values on each side of the two points Represent the proportion between the paper and the distance pitch distance; thus, "1:24 000" means "1 Paper unit represents 24 000 field units "," paper 1 meter field represents 24,000 meters, "or"1 centimeter paper represents 24 000 centimeters ground, "etc.
The scale of the map can be expressed in several ways, either as a fraction (1:50 000), as written expression (one centimeter equals 500 meters) or graphically.

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Echelle 1/50 000

The map scale indicates a distance reduction rate data to be shown on the map.
In general, small-scale maps describe large land surfaces but have a spatial resolution low, showing little detail. By against the large-scale maps represent small surfaces marker, but have a high spatial resolution, showing details.

Entities on small cards
scale represent more fairly the real world entities because of the reduction factor smaller than for a large scale. When the map scale decreases, the entities must be simplified or not be shown at all.

 For example, at a scale of 1: 100,000 (1 cm = 1 km), it is difficult to represent the entities whose length or width is less than 100 meters, because they would 1 mm long and wide on the map.

The relative position of entities in space determines their spatial relationships GIS software can exploit the spatial relationships between entities

-The casino is adjacent to it/the beach ?-How far apart/Hotel Casino?-Which hotels located within 500 m Of the beach

The spatial relationships between geographic features are based on the location of entities. These relationships implied on Map communicate information to the user.
For example, "there is a creek through a park from east to west and the park is adjacent to a forest. " Some types of relationships that can be highlighted:

•  Connectivity: Describes (s) link (s) between different map features (eg the. Fire hydrants are connected to water pipes.)

•  The adjacency: Describes the adjacent entities (around) to another (eg the area. the pavilion is adjacent to a park.)

•  Proximity: Describes the entities that are close to another entity (eg, the home is located near a stream.)

•  The intersection: Describes the entities that intersect (cross) other (eg line. Railway intersects the main street.)

•  The capacity: Describes the entities that are located in a surface (eg shelter is located. inside a park.)

•  The relative position. Describes the relative position between entities (eg, the park is located in the North West of the city.)

•  The altitude difference. Describes the difference in height between entities (eg safeguard Forest is located above the river.)

These relationships can be used to find useful information on a map. For example:

•  Determining a favorable site for landfill waste which must not be located near a stream or a residential area.

•  Determine the best route between a fire station and a home.
•  Find the areas that can be observed from a particular position.
•  Visualize land use in a given area.