Developing Spatial Awareness :-

Transcription

1 Developing Spatial Awareness :- We begin to exercise our geographic skill by examining he types of objects and features we encounter. Four different spatial objects in the real world: Point, Line, Areas and Surfaces. Inside the GIS, real-world objects will be represented explicitly by three of these objects. (Point, line and area). In GIS all data are explicitly Spatial. 1. Point Point features are spatial phenomena, each of which occurs at only one location in a space. (You can easily recognize such feature as houses, tree, road interaction and many more). Each feature is said to be discrete. These features are assumed to have no spatial dimension, no length or width although each can be represented by its locational coordinates. Points then are said to have 0 (Zero) dimensionality. The points will always occur at distance location with no overlap. 2. Line Liner or Line objects are conceptualized as occupying only a single dimension in our coordinate space. These One-dimensional objects may be roads, rivers, regional boundaries, fences or any kind of objects that is fundamentally long and very skinny. Eventually they look so skinny that is impossible to imagine that they are anything but essentially liner object. It also become impossible to represent them as more them lines because we are so far always that we can no longer measure them. Liner object, unlike point objects, allow us to measure their spatial extent by simply finding out hoe long they are. In addition, since they are not sited at a ingle location in a space, we must know at least two points, a beginning and ending point, to describe a location in a space of a given liner object. The more complex the line the more points we need to indicate exactly where it is located. Because we have included a geometric dimension, we can also measure the shapes and orientations of liner object. Page : 1

2 3. Area Objects observed closely enough to be clearly seen to occupy both length and width are called area. Examples of area of two-dimensional objects include a area occupied by a yard, the areal extent of a city, and an area as large as a continent. To describe the locations of area in a space, we recognize that they are composed of the series of lines that begin and end at the same location. With the area we can now describe the amount of territory they occupy. Adding the dimension of height to our area features allows us to observe and record the existence of surfaces. Although we could certainly observe the house at close range and describe it in terms of its overall length and width, we often want to know whether it is a one-story or two-story structure. In this way we need to observe a house not as an area but rather as a three-dimensional object, heaving length, width and height. Surface occurs all around us as natural features. Hills, Valley, Ridges, Cliffs and other features can be describe by citing their location, the amount of area they occupy, how they are oriented, and now, with the additional of third dimensional, can be describe their heights. Because of heights of three dimensional object varies from one place to another, we can also measure the amount of change in height with a change in distance from one degree to another. With this information in a hand we can also determine the volume of material contain in the feature. Spatial Measurement levels :- The spatial objects themselves are called an entities, and as we have seen, they have associated with them a set of coordinates that allows as to describe where they are located. All these spatial features or entities we observe, contain information not only about how they are occupy space but also about what they are and how important they are. For example, a tree viewed as a point feature, we can also investigate the age of that tree. The additional non-spatial information helps us to describe the objects we observe in a space called attribute features. Formally, there is already a well-established measurement framework for nearly all forms of data, including geographic data, this is called the Levels of Geographic Data Measurement. Page : 2

3 The measurement directly allows us to compare the quality of different objects. The measurement levels we use will be determine by: What we are classifying. What we want to know Our ability to make measurements at our selected scale of observation. The first level of measurement is the nominal scale. These are named data. The system allow us to make the statement about what to call the object, but it does not allow direct comparison between one named object and another. If we want to compare two objects we must be more precise in our level of measurement. If we want to be more precise in our measurements, we moved to the Interval level of data measurement, in which numbers are assigned to the items measured. A good example of spatial data measurement at this level consists of soil temperatures across a study area containing widely different soil. We may find the temperature of some very dark, organic-soils is much higher than those for other parts of our study area that lace organic material and are light color. For example the dark soil might have 85 o F while the lighter may have only 77 o F. We now have an easily measured, difference between the soils at two different locations. In limitation is there in the comparison made using this level of measurement. Page : 3

4 For example 50 o F, 100 o F the difference is twice but if we convert the Fahrenheit to the Kelvin scale it would become 283 K and 311 K. So here the difference is not the twice compare t the previous one. So the solution of this data measurement level is to use ratio level data measurement. Spatial Location and References :- Until now we have indicate that we can locate objects in a space. Location is the first important spatial concept we need, but to locate the object means that we must have a structured mechanism to communicate the location of each object observed. First type of location is called Absolute Location and will give us a definitive, measurable fixed point in space. But first we must have a reference system against which to evaluate such a location. The earth is a roughly spherical object with some large-sale and some smallscale deviations from the shape. Around that spherical shape we can use simple geometry to create a spherical grid system. -: The Geographic Grid :- Spherical Grid System showing Parallel and Meridian. Parallels allows us to measure angular distance north and south (Latitude) from the Equator (0 Degree Latitude) up to maximum of 90 degree North (North Pole) ad 90 degree South (South pole). Meridian starts at the Prime Meridian and allows us to measure angular distance east and west (Longitude) up to maximum of 180 degree where they would meet at the international date line. At the Equator the starting of first Parallel Line, we assign a starting value of 0. So we can measure an angular distance from the equator north or south up to a maximum value of 90 degree. Page : 4

5 This system of angular measurements allows us to state an absolute location of any point on the earth by simply calculating the degree of latitudes north and south of the equator and the degree of longitude ease and west of Prime Meridian. Page : 5

6 Chap. 2 : Basic Geographic concepts These angular measurements can readily be converted into Feet or Miles, Meters or Kilometers, thus allowing us to measure a short or long distance on the ground using device designed for calculating them. To find the Great Circle distance D between two point on earth :- Point A :- Latitude = N, Longitude = W Point B :- Latitude = N, Longitude = W cos D = (sin α * sin β) + (cos α * os β * cos δλ ) Where : o α and β are the geographic latitude of Point A and B. o δλ is the absolute value of the difference of the geographic longitude of point A and B. cos D = (sin 63.5 * sin 25.75) + (cos 63.5 * cos * cos ) cos D = (0.895 * 0.434) + (0.446 * * ) cos D = cos D = (D = cos = ) 69 Miles per 1 0 Degree D = * 69 = 4488 Miles But as we continue to explore our world, it would be very useful to be able to describe not only the absolute address but also the relationship among the objects. This Relative Location becomes the quit famous in our GIS analysis. With our absolute grid system we can determinee relative locations b knowing the absolute distance between any two objects by simply subtracting the coordinates of the small from the large. Relative distance is only half of what we might want to know. It would also be useful to know the difference in direction between the two objects. (X2 X1) = Difference in Longitude (Y2 Y1) = Difference in Latitude Pythagorean Theorem Spatial Patterns :- Many features and objects occur in far greater numbers: cites in a country, houses in a cities, animals in natural areas, natural areas in states, trees in a forest, roads across nations even plants in gardens al occur in as multiples. But they do not all occur uniformly located within this area. Each set of objects exhibits a particular spacing or set of arrangements. Page : 6 ajay @gmail.comm Mobile:

7 We being to notice that these arrangements and spacing seem to have underlying controls or processes that dictate their placement. By following the direction, we produce a regular or uniform pattern of evenly spaced planets. This uniform pattern differs considerably from the locations of the tree in the forest, which seems to be scattered at random, with no apparent underlying design. A clustered distribution of cities demonstrates a type of distribution with high density of features, where as the distribution of other objects such farmhouses, scattered about a nation s rural land space, demonstrates a more dispersed pattern. One spatial pattern may be partially or totally related to some other spatial pattern. We can now begin to ask questions about the causes not only a single distribution but also spatially correlated distributions of phenomena. This is among the more powerful capabilities of modern GIS. Geographic Data Collection :- Two general methods are there for observing the data :- 1. Ground survey method. 2. Visual observation. Observations such as qualitative or categorical data are still acquired by means of direct visual observation or by collection of sample specimens for later identification. These observations should be evaluated carefully before they are accepted as truth since often their quality is a function of observer s experience. Devices used for the observation :- Compass, Plan Table and Alidade. Methods for measuring the distance :- From the point of known location, surveyors can measure distances and angles through a process called Dead Reckoning. Page : 7

8 In navigation, dead reckoning is the process of calculating one's current position by using a previously determined position. In geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres. In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline. Differences in the elevation at different on the landscape and be measured with the use of a device called a Dumpy Level, which has a telescopic sight much like the alidade but is place on the taller stand and is capable of rotating up and down to examine the elevation differences at a distance. Technological innovations have improved the methods by which we can obtain positional information, especially for a large portion of earth How satellites communicate? Circling the globe today satellites, whose positions are known with great accuracy? The satellites receive a ration transmissions from field unit on earth and return a signal that is processed by a near by ground station and is then send to the field unit as a set of coordinates. The coordinates gives us positional location as well as elevational location providing a very useful data to the users. A recent trend in this form of spatial data collection, called radio telemetry. Telemetry is a technology that allows remote measurement and reporting of information. The word is derived from Greek roots tele = remote, and matron = measure. Systems that need external instructions and data to operate require the counterpart of telemetry. As these two technologies (Land Observation & Radio Telemetry) continue to improve in quality, ease of use and the cost there will be more and batter data available for later input to our GIS. When our concern is to gather the information about the distribution of objects, plants, animals or even people rather then individual locations, we employ another from data collection called census. Then census device depends up on the nature of the data to be collected. Page : 8

9 We might use a direct contact to physically note the exact location and characteristics of individuals in small areas. The purpose of these methods is to obtain information about an entire population of object in a space. (e.g. Census Conduct by the Government) Such a survey devices attempt to gather both locational and attribute data so that generalization can be made about the population. Remote Sensing :- Obtaining the data about phenomena on the regional or even the continental scale may require the use of secondary or indirect method of data collection called Remote Sensing. Remote sensing refer to the use of satellites that obtain the data about the surface of large regions of the planet, commonly in the form of computer-compatible data that can immediately be operated on by computer software. Aerial Photography :- A mainstay (આધ ર) in the wild range of spatial analyses, is a long tradition of a use for forest and range evaluation and management because the photos allow analysts to see substantial areas at a glance. The soil scientists have used the aerial photographs to assist in perceiving the subtle changes in soil type over large areas. Urban specialists have used aerial photographs to estimate the population by counting dwellings ( નવ સ) for known average per household. The military, of course, has used aerial photography for sometime as a mean of reconnaissance (for searching enemies). Similarly, a number of more exotic airborne devices such as Side Looking Airborne Radar (SLAR), Scanning Radiometers, Color Video and Digital Photography tend to ruled out for large scale applications Page : 9