United Arab Emirates UniversityCollege of Humanities and Social Sciences

Geographic Info. Systems (1)

CHAPTER 4

Content ..

1)4.1 Introduction..2)4.2 Placenames..3)4.3 Postal Addresses and Postal

Codes..4)4.4 linear Referencing System..5)4.5 Casters and the US Public Land

Survey System..6)4.6 Measuring the Earth: Latitude

and Longitude.. 7)4.7 Projections and Coordinates..8)4.8 Converting Georeferences..9)Conclusion..

4.1 Introduction..

• Time is an optional element in geographic information but location is essential.

 • To be most useful georeferences should stay

constant through time.

• Metric georeferences are much more useful because they allow distances to be calculated.

4.2 Placenames..

• Many commonly used placenames have meaning that vary between people and with the context in which they are used.

• The meaning of placenames can become lost through time.

4.3 Postal Addresses and Postal Codes..

• We use postal addresses in many aspects in our life like: delivery of mail, place of residence.

• Many GIS application rely on the ability to locate activities by postal address, and to convert addresses to some more universal system of georeferencing.

• Postal addresses work well to georeference dwelling and offices, but not natural features.

• Postal codes have proven very useful for many purposes besides the sorting and delivery of mail.

• Most people know the postal code of their home, and in some instances postal codes have developed popular images.

4.4 linear Referencing System..

• Linear referencing system are widely used in managing transportation infrastructure, and in dealing with emergencies.

4.5 Casters and the US Public Land Survey System..

• The Public Land Survey System defines land ownership over much of western North America, and is a useful system of georeferncing.

4.6 Measuring the Earth: Latitude and Longitude..

• The Earth is slightly flattened, such that distance between the poles is about 1 part in the 300 less than the diameter at the Equator.

• Lines of latitude and longitude are equally far apart only that Equator; towards the poles line of longitude converge.

4.7 Projections and Coordinates..

• Although nothing in a digital computer is flat, there are several good reasons for using projections in GIS to flatten the Earth.

• Two datasets can differ in both the projection and the datum, so it important to know both for every dataset.

• When longitude is assigned to assigned to x and latitude to y a very odd –looking Earth result.

• It is wise to be careful when using a GIS to analyze data in latitude and longitude rather than in projected coordinates, because serious distortions of distance, area, and other properties may result

• UTM coordinates are in meters, making it easy to make accurate calculation of short distances between points.

• All US states have adopted their own specialized coordinate system for application such as surveying that require very high accuracy.

4.8 Converting Georeferences..

• Methods of Converting between Georeferences are important for:

o Converting lists of customer addresses to coordinates for mapping or analysis..

o Combining datasets that use different systems of georeferenceing..

o Converting to projections that’s have desirable properties, e.g. no distortion of area, for analysis..

o Searching the Internet or other distributed data resources for data about specific locations..

o Positioning GIS map displays by recentering them on places of interest that are known by name ( these last two are sometimes called location services )..

Conclusion..

• This chapter tell us about important elements of the geographic information . First, The location is necessary of it . Metric georeferences are much more useful .Also, we must use the placename and use postal addresses in many aspects in our life. In addition, Lines of latitude and longitude is important to determine places or times .

THE END