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Geography 70

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Geography 70

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    1. 9/10/2012 University of Memphis, Dr. Taff 1 Geography 70

    2. 9/10/2012 University of Memphis, Dr. Taff 2 Representing the Real World Real World Map Since GIS is based on the model of a map, we have covered elements of maps up to this point. If you remember back a few lectures, I said that the three elements of a map are scale, projection and symbolization. Weve talked about scale. Weve covered projection and the elements that go along with it: geodesy and coordinate systems Now, we come to symbolization.Since GIS is based on the model of a map, we have covered elements of maps up to this point. If you remember back a few lectures, I said that the three elements of a map are scale, projection and symbolization. Weve talked about scale. Weve covered projection and the elements that go along with it: geodesy and coordinate systems Now, we come to symbolization.

    3. 9/10/2012 University of Memphis, Dr. Taff 3 Symbolization In a GIS, we represent real world phenomena in a digital format

    4. 9/10/2012 University of Memphis, Dr. Taff 4 Vocabulary Entity Data objects

    5. 9/10/2012 University of Memphis, Dr. Taff 5 Terminology Entity -- a real world phenomenon to be represented in a database There are some terms that you need to know that help describe how this real world-to-digital data conversion takes place. Real world phenomena are known as entities. Some entities might be: Buildings Forest Roads Coastline Pastures Pasture boundaries Entities are the geographic objects in the real world that we want to represent in the GIS. Now keep in mind, like Ive talked about before, there are two components to geographic data: location and attributes. We may create a representation of this road by drawing a line and assigning real world coordinates to it. However, there are features, information, attributes of the road that also need to be assigned. Speed limit and surface type may be important attributes. Keep this in mind as I go along here. There are some terms that you need to know that help describe how this real world-to-digital data conversion takes place. Real world phenomena are known as entities. Some entities might be: Buildings Forest Roads Coastline Pastures Pasture boundaries Entities are the geographic objects in the real world that we want to represent in the GIS. Now keep in mind, like Ive talked about before, there are two components to geographic data: location and attributes. We may create a representation of this road by drawing a line and assigning real world coordinates to it. However, there are features, information, attributes of the road that also need to be assigned. Speed limit and surface type may be important attributes. Keep this in mind as I go along here.

    6. 9/10/2012 University of Memphis, Dr. Taff 6 Terminology Data Object -- digital representation of an entity So you have your Entities, your real world objects that you want to put into the GIS. Entities are represented by Data Objects. A data object is So you have your Entities, your real world objects that you want to put into the GIS. Entities are represented by Data Objects. A data object is

    7. 9/10/2012 University of Memphis, Dr. Taff 7 Summary Data objects represent entities in a GIS. So to summarize, you have a data model that is made up of data objects, each of which represents a real world entity. So to summarize, you have a data model that is made up of data objects, each of which represents a real world entity.

    8. 9/10/2012 University of Memphis, Dr. Taff 8 Topology The relationships between data objects in space. This relationship between objects in space, whether conceptually or logically, is known as topology.This relationship between objects in space, whether conceptually or logically, is known as topology.

    9. 9/10/2012 University of Memphis, Dr. Taff 9 Conceptualizing Topology Adjacency Connectivity Containment Direction Proximity Overlap There are three primary components of topology. They are adjacency, connectivity and containment. There are also two other components that are important, but I consider them secondary components of topology. They are direction and proximity Can anybody give me a definition of adjacency? Just give it a shot. Its not a special definition. How about connectivity? OK. What about containment? Direction is easy. Everyone knows where north is, right? Or do you? Im going to do a quick test. Im going to ask you which direction north is in from here. I will mention four landmarks around here. Everyone put your heads down. Now raise your hand if you think the Carolina Inn is north of here. Raise your hand if you think the Post Office downtown is north of here. Raise your hand if you think the Forest Theater is north. Raise your hand if you think Kenan Stadium is north. (Tally votes) See, not everyone inherently knows directions. When objects have a topological relationship, their direction in relation to each other can be determined. OK. Now, how about a definition of proximity. Good. Now, Im going to go through these using an example that everyone should be familiar with. And I have to give credit where credit is due. John Spencer came up with these examples and Im borrowing them from him.There are three primary components of topology. They are adjacency, connectivity and containment. There are also two other components that are important, but I consider them secondary components of topology. They are direction and proximity Can anybody give me a definition of adjacency? Just give it a shot. Its not a special definition. How about connectivity? OK. What about containment? Direction is easy. Everyone knows where north is, right? Or do you? Im going to do a quick test. Im going to ask you which direction north is in from here. I will mention four landmarks around here. Everyone put your heads down. Now raise your hand if you think the Carolina Inn is north of here. Raise your hand if you think the Post Office downtown is north of here. Raise your hand if you think the Forest Theater is north. Raise your hand if you think Kenan Stadium is north.(Tally votes) See, not everyone inherently knows directions. When objects have a topological relationship, their direction in relation to each other can be determined. OK. Now, how about a definition of proximity. Good. Now, Im going to go through these using an example that everyone should be familiar with. And I have to give credit where credit is due. John Spencer came up with these examples and Im borrowing them from him.

    10. 9/10/2012 University of Memphis, Dr. Taff 10 Adjacency Adjacency this relationship describes whether or not two objects are next to one another In this example, Springfield and Shelbyville are adjacent. In the real world, France and Germany are adjacent; France and England are not.Adjacency this relationship describes whether or not two objects are next to one another In this example, Springfield and Shelbyville are adjacent. In the real world, France and Germany are adjacent; France and England are not.

    11. 9/10/2012 University of Memphis, Dr. Taff 11 Connectivity Connectivity are two objects connected? Here, Springfield is connected to South Springfield. Real World #1 (lines): Franklin St and Columbia are connected. They intersect. Real World #2 (areas): Chapel Hill and Raleigh are connected by I-40 Are they adjacent? No. But, Springfield and South Springfield are both connected and adjacent. So what is the difference, if any? Well, lets take this adjacency vs. connectivity a step further. I may confuse you on this, but I just want to try and reinforce this idea. But it may only confuse you further. Think back to before the fall of the Berlin Wall. West Berlin and East Berlin were adjacent. But were they connected? Well, yes, there was a gate through the wall, but without the proper papers, you could not pass through it. So, for the majority of Berliners, the two cities were not connected. But they were definitely adjacent. Now, lets think of England and France. They are definitely not adjacent. The English Channel separates them. But they are connected. We can say they are physically connected, because the Chunnel (the underwater tunnel) connects them.Connectivity are two objects connected? Here, Springfield is connected to South Springfield. Real World #1 (lines): Franklin St and Columbia are connected. They intersect. Real World #2 (areas): Chapel Hill and Raleigh are connected by I-40 Are they adjacent? No. But, Springfield and South Springfield are both connected and adjacent. So what is the difference, if any? Well, lets take this adjacency vs. connectivity a step further. I may confuse you on this, but I just want to try and reinforce this idea. But it may only confuse you further. Think back to before the fall of the Berlin Wall. West Berlin and East Berlin were adjacent. But were they connected? Well, yes, there was a gate through the wall, but without the proper papers, you could not pass through it. So, for the majority of Berliners, the two cities were not connected. But they were definitely adjacent. Now, lets think of England and France. They are definitely not adjacent. The English Channel separates them. But they are connected. We can say they are physically connected, because the Chunnel (the underwater tunnel) connects them.

    12. 9/10/2012 University of Memphis, Dr. Taff 12 Containment Connectivity describes objects that may be wholly contained within an area Springfield contains Moes, the Kwik-E-Mart, and the Nuclear Plant Real World: University Lake is contained within the area of Orange CountyConnectivity describes objects that may be wholly contained within an area Springfield contains Moes, the Kwik-E-Mart, and the Nuclear Plant Real World: University Lake is contained within the area of Orange County

    13. 9/10/2012 University of Memphis, Dr. Taff 13 Direction Direction. This is a human derived attribute. Direction is relative. Therefore, it is an important conceptual part of topology, but as you will see in a minute, it is not an important logical part of topology.Direction. This is a human derived attribute. Direction is relative. Therefore, it is an important conceptual part of topology, but as you will see in a minute, it is not an important logical part of topology.

    14. 9/10/2012 University of Memphis, Dr. Taff 14 Proximity Proximity how near certain objects are to each other, or far away from each other they are This is another relative measure. Once again, it is conceptual, not logical. It is also a derived measure. A GIS does not inherently know which objects are near each other. It is a subjective determination. Real Sesame Street kind of stuff, but they are important measures used in geographyProximity how near certain objects are to each other, or far away from each other they are This is another relative measure. Once again, it is conceptual, not logical. It is also a derived measure. A GIS does not inherently know which objects are near each other. It is a subjective determination. Real Sesame Street kind of stuff, but they are important measures used in geography

    15. 9/10/2012 University of Memphis, Dr. Taff 15 Overlap Adjacency this relationship describes whether or not two objects are next to one another In this example, Springfield and Shelbyville are adjacent. In the real world, France and Germany are adjacent; France and England are not.Adjacency this relationship describes whether or not two objects are next to one another In this example, Springfield and Shelbyville are adjacent. In the real world, France and Germany are adjacent; France and England are not.

    16. 9/10/2012 University of Memphis, Dr. Taff 16 Review The relationships between data objects in space. This relationship between objects in space, whether conceptually or logically, is known as topology.This relationship between objects in space, whether conceptually or logically, is known as topology.

    17. 9/10/2012 University of Memphis, Dr. Taff 17 Entities in the real world are represented as one of the following in a GIS: Vector data: Points Lines Areas (or polygons) Raster data Pixels in an array 2 GIS Data Models

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    20. 9/10/2012 University of Memphis, Dr. Taff 20 Raster data model (details later)

    21. 9/10/2012 University of Memphis, Dr. Taff 21 Raster data example

    22. 9/10/2012 University of Memphis, Dr. Taff 22 The vector data model

    23. 9/10/2012 University of Memphis, Dr. Taff 23 Vector Data Objects Geographic building blocks Points 0 dimensional Lines 1 dimensional Polygons 2 dimensional The vector model is composed of three basic spatial objects, known as geographic primitives. They are known as this because they are the basis of geographic entities.The vector model is composed of three basic spatial objects, known as geographic primitives. They are known as this because they are the basis of geographic entities.

    24. 9/10/2012 University of Memphis, Dr. Taff 24 Spatial Objects

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    26. 9/10/2012 University of Memphis, Dr. Taff 26 Thought question: How are you going to represent the California OAK tree in digital format? A point? A polygon? Or a pixel? It will depend on: Scale of observation Purpose of your research The type of data you have access to in the GIS

    27. 9/10/2012 University of Memphis, Dr. Taff 27 Thought questions:

    28. 9/10/2012 University of Memphis, Dr. Taff 28 The vector data model represents geographic features similar to the way maps do A point: recorded by a pair of (x,y) coordinates. A line: recorded by joining more than one point, A polygon: recorded by a joining multiple points that enclose an area

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