Understand the three perspectives of GIS:
GIS is a system for managing, analyzing, and displaying geographic information. Geographic information can be expressed through a series of geographic data sets. The geographic data set is modeled by using simple, ordinary data structures. GIS contains a comprehensive tool for handling geographic data.
We can understand how the geographic information system works from geographic information from multiple perspectives:
1. From the perspective of spatial database: GIS is a spatial database that includes data sets for expressing universal GIS data models (elements, grids, topologies, networks, etc.).
2. From the perspective of space visualization: GIS is a smart map while also a view for displaying the elements and elements between the surface. The geographic information of the underlying can be expressed in a variety of maps, and these expressions can be constructed as a "database window" to support query, analysis, and information editing.
3. From the perspective of spatial processing: GIS is a set of information conversion tools for getting new data sets from existing data sets. These spatial processing functions extract information from existing data sets, and then analyze, and finally import the results into the data set.
These three views use ArcCatalog in ESRI ArcGIS (GIS to be a set of geographic data sets), ArcMap (GIS is a smart map) and Arctoolbox (GIS is a set of spatial processing tools). These three parts are key content that make up a complete GIS and is used for all levels in all GIS applications.
From the perspective of the spatial database:
GIS is a unique database-spatial database (GEODATABASE). It is a "used for geographic information systems". Fundamentally, GIS is based on a structured database that uses geographical terms to describe the world.
Here we review some basic principles in the spatial database.
Geographic expressions
As part of the GIS space database design, the user wants to specify how the elements are reasonable. For example, the plot is usually expressed in a polygon, and the street is in the form of centerline in the map, and the water well is shown. These elements will form elements, each of which has a common form of geographic expressions.
Each GIS data set provides spatial expression on a certain aspect of the world, including:
Vector elements based on vector (point, lines and polygons)
Grid data set such as a digital elevation model and image
The internet
Terrain and other surfaces
Measuring data set
Other types of data, such as address, place name, and mapping information
Descriptive properties
In addition to geographic expressions, geographic data sets also include traditional description geographic objects. Many tables and spatial objects can be related to each other by the fields they share (also known as "keywords"). As they are in traditional database applications, these information sets and information relationships in the form of forms play a very critical role in the GIS data model.
Spatial Relations:
Topology and cyberspace relationships, such as topologies and networks, are also an important part of a GIS database. Using topologies is to manage common boundaries, definition, and maintenance data between elements, and support topology query and roaming (such as determining the neighborhood and connectivity of elements). Topology is also used to support complex editing, and build features from unstructured geometry (for example, using lines to build polygons).
Geographical elements share geometric shapes. The geometry of the elements can be described using the relationship between nodes, edges, and face.
The network is a diagram describing a GIS object that can penetrately penetrate. This is important for analog paths and transportation, pipelines, equipment, hydroxation, and other network-based applications.
In this web example, the street elements represent the edges of their endpoints (called "connection"). The steering model can be used to control the communication from one side to the other side
Feature layer and data set:
GIS organizes spatial data into a series of topic layers and forms. Since the spatial data set in GIS has a geographic reference, they have the location information of the real world and superimpose. GIS integrates multiple types of space data
In a GIS, the same type of geographic object set is organized into a layer, such as a plot, well, building, orthodontic image, and grid-based digital elevation model (DEM). Clearly defined geographic data sets are quite important for a practical geographic information system, while the topic information collection uses layers to organize, such thoughts are also a key idea of GIS dataset.
Data sets can be used to express:
Original measurement (such as satellite images)
Interpreted information
Data from spatial analysis and modeling
Through the common geographic location between the layers, we can easily get the spatial relationship between multiple layers.
GIS uses ordinary object classes to manage these simple layers, while gaining key contacts between data layers with a functional tool.
GIS will use a large number of data sets that are usually from different organizations and have various manifestations. Therefore, it is important for the GIS data set:
Use simple and easy to understand
Easy to use other geographic data sets
Can be effectively edited and verified
Ability to form a clear document with clear documentation, use and objective description
Any GIS database follows these common principles and concepts with file-based data organization. Each GIS requires a mechanism to describe the geographic data in accordance with these principles, and uses a comprehensive tool to use and manage this information. (to be continued)
