Spatial Data Structure in GIS | Alemayehu Midekisa | Skillshare
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3 Lessons (16m)
    • 1. Welcome!

    • 2. Spatial Data Structure

    • 3. Resolution of Spatial Data

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About This Class

In this class, we will discuss about the different data structures in a GIS. The two main spatial data structures in a GIS are vector and raster data models. We will talk about the advantages and disadvantages of both data models with example data. We will use the QGIS software for this class. 

Meet Your Teacher

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Alemayehu Midekisa

Geospatial Data Scientist


Dr. Alemayehu Midekisa (PhD) is a research scientist at the University of California San Francisco. He has a Master of Science degree in GIS and Remote Sensing and a PhD in Geospatial Science & Engineering. Dr. Midekisa is also the recipient of the prestigious NASA Earth and Space Science Fellowship and various other awards. He has over 10 years of experience applying geospatial science and technologies in various applications including public health, agriculture, and natural resources.

His research work in the application of geographic information science has been published in various scientific journals. He has presented his research findings in various scientific meetings including the American Geophysical Union, Association of American Geographers, American Tropical and Hygiene and Medicine, and NASA Science Team Meetings. He teaches online courses in various themes including geospatial science and technology. He is also the founder of Nile Geospatial.

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1. Welcome!: Hey, Al Amal, you're here. Today, we're going to be learning about structure of spatial data. We'll start off first by discussing the two main special data models, which includes the victor and Raster data models will also look at the advantages and disadvantages of each of the state of models. Will also do practical exercise on how toe access and visualize the satellite data using open source software Tool called QG eyes also compare high and low special resolution satellite data in a queue Jack's platform. 2. Spatial Data Structure: hi and this lecture Learn about special data models well, first started by exploring raster and Vector data models, we'll then see the advantages and disadvantages. Suppose Raster and Vector data models finally wrap up this lecture by discussing Time medical really of different layers and a geographic information system or a G ice. Special data come represents rewarded features that have discrete boundaries that just rots buildings, legs and rivers, as well as reworded, phenomenon or features that have nondescript boundaries. For example, rainfall, temperature and terrain Roster is a senior biz data structure composed off rose and columns for storing image margins. Units are called cells, or pixels. Victor is a coordinate based data structure commonly used to represent the geographic features. More genius feature units are points, lies and polygons. In a victor data model, a Raster data model used a great and every cell in that greed has a volume, and that cell can hold a number or index of always standing for into bits. Assent as a special resolution. Special resolution of a cell is the size off that sale picture result ocean in a ground unit, for example, for a lots us all that image. The special resolution is a certain mater, which means a single pixel and on imagery represents a certain matter by setting certain meter area on the ground. This is an example of a raster data, which is a continues elevation. Raster was darker shaded areas for Heil elevation. First light for lower in division that shows a map off the U. S. A. In terms were presented in terms of digital elevation model Roster data has different special resolution. For example, as you can see here on the left side, you have a lance, a satellite image which has a certain matter special resolution. That means every pixel represented in the A major corresponds to a certain matter by certain mater area on the ground, whereas the higher resolution image from digital globe, which is lives on 10 meter, a special resolution. So if you compare it to AIM, is to represent a similar area. But on the higher a special resolution image on the right side, you can see more detail. For example, you can see the stadium buildings, rods and you know other building areas. For example, church. You can identify where us on the left side the lands that image a moderate resolution image , which is a pretty good one, but not as detailed. US the the one on the right side, so moderate to lower Special results Image would not give us a smudge detail as the high spatial resolution image on the right side. So, um, when it took about raster motor, there are different elements of raster data model. The 1st 1 is a cell volume, so each cell in a raster carries the volume, which represents the characters tooks. The character sticks off a special phenomena at the location donated by its role and colon . The sale value can be an integer, or it can be a floating point, and another element of raster data is the sail size, so the sale size determines the resolution off the Raster data model. Another element is a bund, a roster bunt, so Rester may have a single button or multi buns. Next special reference. So a raster did. I must have the special reference information so that they can ally, especially with other data sets in a geographic information system or G ice. So this air virus examples off raster data, as you can see on the top. It's a satellite image on an a T the middle you have terrain or a digital innovation model . Another example of a raster data goes off. Ah, land use land cover map, which sometimes can be represented us a. Raster data or sometimes us Ah, Victor did, depending on how that data is represented so it can be represented both in a victor. A roster data model. Ah, and the other data type is a Mariah data. This is deters risk. Map mostly can be represented. Us. A. Roster did immortal, so thrusters and victors of advantage. So let's start with a raster data. So what are the advantages of Forester data? It's simplistic data structure, and it's easy for overly analysis. Ah, and verse kinds of specialists can be performed, and also it has a uniform size and chip. You know, however, it has some limitations. So the limitation of a raster did. It can be, you know, it's really hard to store, so storage is really difficult and expensive because it's a large amount of data and projection and transformation. Prediction, transformation or projection. Corn. A system is difficult compared to Victor data model and different skills between layers can be a nightmare. That means, for example, if you're doing some analysis using ah high especial resolution image. For example, Sentinel Satellite was coarse resolution data from Mahdi's. You know, doing some overly announced or special allowances in those two data would be pretty much difficult because they're not understand special resolution, and you may lose some information to the generalization. So these are the advantages and disadvantages of arrested. Let's get back to a vector data model. So there are streaming geometric shapes, and the victor didn't move. So the 1st 1 is a point and line and polygons. So the advantages and disadvantages of Victor denim ALS The advantage is a good representation of reality and its compact data structure. That's pretty, you know, pretty cool for for data storage and what have you and also has a topology feature, which can be described in the note network analysis. And it can also provide a pretty accurate graphics. Whereas there are some advantages this wall. So the 1st 1 is it has complex data structure, unlike the rest, their data and in simulation, maybe difficult in ah Victor data model and finally some special analysis is difficult, especially overlay analysis is much easier using a raster data motor. So that's ah, limitation of vector data. More finally, the advantage to a geographic information system is that because there is a special reference system or projection, we can overlay various data layers. For example, here we can overlay, um, various location based information such a streets and address and also even parcels Additionally, we can integrate was Vector and raster did a model in a geographic information system. In this case, for example, elevation zoning. So we can overlay into virus overly analysis and to answer, um, special problems or complex, you know, problems that deal with, um ah, space or a special and analysis, or just that does location best information. So geographic information system is amazing plot from to store overlay and analyse and answer rewarded special problems 3. Resolution of Spatial Data: Hi. In this video, you learn about the special resolution off satellites. Satellites have different special resolution, high medium and low resolution. So in or in this case, we'll explore the Sentinel landside satellite and also the DigitalGlobe high resolution image from Googlers. Now let's get started first, let's adding the landside satellite image is in clears uglier and addressed earlier. Bay Area Lanza RGB. So we averted the landside image, which has a certain it a special resolution. Now let's start in the second satellite image from sentinel sensor layer. Add layer and add rust earlier. And the next thing is to How do you know plugging so that will be able to access high resolution imagery. Flum Googlers To do that, Add the plaguing called opal ears. Because I have already installed the operators plugging. It shows me here in your kids. If you have not already installed the open air plugging, install it and often it I'll close this. I'll just directly goto Web and all Pallares plugging, which is already installed, and Google Maps. We have different options Google physical Streets, hybrid and satellites. So, in this case, because I want to see the satellite image all choose Google Satellite. No, my Google satellite maps are added into Q Jays. It's rearranged the order. I'll put the lands of satellite Bay Area landside RGB on the top, and a 2nd 1 is the Sentinel Image. Bay Area is to sentinel to RGB at the bottom. I'll just add Google Satellite image. No, we have three different satellite image with three different resolution. The 1st 1 is course special resolution. The Landside satellite image, which has a 30 meter special resolution that means image on the ground are represented. Other certain 30 meter pixel resolution within a landside image. Where is the 2nd 1? Is the Sentinel image, which has a 10 meter special resolution? That means each pixel represents a 10 meter by 10 meter unit on the ground, and the Google satellite image are mostly listen one meter. They're very depending on where you can see some areas have some years off the world have on Googlers. They're high resolution about Lizana meter in some places, a little more than a mater. So let's go explore. This is a big area image, so let's go to San Francisco Airport to do that, I'll use the pond in the zoom buttons here that's assuming to San Francisco airport. So within the land sat image, I cannot see clearly the airport, the runways and the different airplanes park it on the runway, and this image is pixelated, and this is a certain native special resolution. So now it's good. Check the second satellite image, the Sentinel Image, which has a 10 meter special resolution. Now I can see the airplanes park it on the air, the runway and also some off the buildings. More clearer compared to the landside image. If I opened the Google satellites mostly DigitalGlobe high resolution image. Now I can see the airplanes, the buildings, other features on the airport. More clearly, I can pan zoom zooming in. Now I can go even in a more detail might take a little time since its loading. So now you have seen three different satellite image was different. Special resolution, The Lancet image or pixelated at a certain it's a resolution. The Sentinel image. 10 metres special resolution, which is better than the land set the Google satellite image, mostly from DigitalGlobe. They're high resolution. So now we have seen three different kinds off satellite image with different special resolutions. You can understand objects on the ground using different satellite image. High resolution satellites are used mostly for surveillance purpose or in infrastructure mapping, whereas moderate to coarse resolution. Satellite in messages. Lance that can be used mostly for land cover mapping and understanding change on the land cover.