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Before diving into ArcGIS, it's important to get an understanding of what exactly a GIS is in the first place. To do this, we first need to delve into the world of map making. Cartography is the art and science of creating maps. The artistic component comes from a deep application of design aesthetics, color theory and legibility concerns. A scientific component requires an understanding of the physical, cultural and environment processes that shape our planet. Cartographers make maps in order to transfer information about the world to the map reader.
And maps are often thought of as a storytelling device. In order to make a map and clarify often complex geographic interactions, a cartographer needs to know something about what is going on in the area of interest. For that we need to gather data and as it turns out we need lots of data. But not just any old spreadsheet of values will help us make a map. For instance, we can pull up a data table about some cities we are interested in telling a story about. We can get their population and the year they were founded. And maybe some statistical information such as the average rainfall inches per year.
And with just this simple table we can start to make some observations. We can see that New York City's population is more than twice that of Los Angeles. Or that Chicago and Seattle were both founded within a couple of decades of each other. We can also dispel the myth that Seattle is a very rainy city. But in fact in receives nearly 20% less rain than New York. Those may all be interesting things to know, but none of this information helps me make a map of these four cities. As an example, would you be able to tell me which city is farthest north? In order to make a map, we need a special kind of data. We need Geospatial Data.
We use the word geospatial to describe any kind of information that has a location component to it. Typically this will be a series of coordinates such as latitude and longitude or the number of feet or meters from a known location like a surveyor's marker. These points can provide a specific location or be grouped into a series of points that describe a boundary line or the perimeter of a closed area. Here I've added some basic latitude and longitude values to our original data table. Latitude is the number of degrees north or south from the equator and longitude is the number of degrees east or west from the prime meridian line.
Which runs from the North to South Pole through Greenwich England. We can now start to make some comparisons about the cities, based on their geography. For instance, we can see that New York is about one degree south of Chicago, and about seven degrees south of Seattle. Or that, from Los Angeles to New York is a distance of about 44 degrees. We can take this one step further and start placing points on the grid. So that we can see distances between cities and their relative positions. Now I can tell that the distance from Chicago to Seattle is about twice that from Chicago to New York. For added context, we can start layering in some additional data, such as the boundary of the United States, and so on.
To further explore our rainfall data that we saw earlier. I would need to gather layer in data on prevailing wind directions, mountain ranges, water bodies, and temperature. As you can tell, investigations into the geography of things can get quite complicated even for a relatively simple study. So geospatial data tells us not only what is happening, it also tells us where it is happening. And as you might expect, interesting things are happening all around us. And all kinds of data about our world are constantly being measured and recorded by various censors, surveys, and studies.
All of this raw information comes in the form of data that needs to be organized. And we'll use a geographic information system or a GIS to do that. A GIS organizes and displays geospatial data. And allows you to manipulate and analyze the results. The main goal of a GIS is to facilitate informed decision making. In the past, a basic geographic information system consisted of organizing data onto transparent sheets of plastic and stacking them together to get a final map. Each component of the map would get it's own sheet for instance parks, roads, buildings and labels would all be separated.
When you view the entire stack, you would then see the relationships between the various features on the finished map. If updates to any one component occurred, say a new building was constructed. Only the building sheet would need to be updated and a new map was produced. Flash forward a few decades and we'll now use computers to handle all the organizational tasks for us. But the concept of keeping separate layers of information still remains. This is the core of what a geographic information system or GIS is all about. It helps you organize databases of information about the location of features in the landscape.
Such as places like city and voting districts or county boundaries. Things such as the location of individual trees or fire hydrants or roads and buildings. Or even event occurrences such as burglaries and bicycle thefts, floods or the location of historical events. Obviously the list is endless. Now that you know what a GIS is and what it's used for it's time to start working with a specific GIS software package, Esri's ArcGIS.
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