Lab #5 Data Source and Management

Stefanie Wieschalla

Geog 206

Part 1:

1. The advantages of using digital spatial data are that it is possible to directly transfer them to other digital devices and GIS systems, where they may be further processed. Digital formats provide a more efficient processing of data. Besides that, it is the easiest, quickest and least expensive source of spatial information. Disadvantages are that the data may not be in the format you want it to be so you need to convert it. Also, global data sets do not really exist because only few governments collect spatial data in the same way or with the same attributes. Data reduction or documentation methods may be different across national boundaries. Furthermore, digital spatial data is only partly available to the public and quality is not always good.

2. The most important question to ask before using already-developed spatial data is regarding its source. Is the data accurate? Who produced it? What are the source materials and what do they contain? Furthermore it is significant to ask if the data is free and if the data matches your theme and scale. Is it appropriate?

3. DOQs differ from regular photographs because they are actually scanned photographic images that have been corrected for distortions due to camera tilt, terrain displacement, and other factors. These corrections yield photographers that are planimetrically correct are very similar to large-scale topographic maps.

4. Digital Raster Graphics (DLGs) have been mostly produced from USGA series maps and most features on these maps have been recorded in DLGs so there is a close correspondence between DLGs and USGS series maps. Hence DLGs are vector representations of most features portrayed on USGS national series maps. They are available by map series designation, for example 1:2 million DLGs are available that contain the data included on 1:2 million scale maps. DLGs for 1:100,000 and 1:24,000 scale maps are also available. The extent of an individual DLG typically corresponds to the extent of the map series.  The materials contain boundaries, hydrography, roads and hypsography.

The U.S. Census Bureau produces and maintains database systems to support the national census. This system is known as the Census Tiger system. It links geographic entities to census statistical data on population size, age, income, health, and other factors. The units are typically polygons classified by roads, streams, political boundaries, or other features. These source material files define line, landmark and polygon features in a topologically integrated manner. Polygon features for example include census tabulation areas such as census block groups and tracts. These files contain information to identify street address labels.

The National Land Cover data has been produced by the USGS and other agencies and organizations to meet a wide variety of spatial needs. The data source materials are based on the interpretation of t1970s and early 1800s aerial photographs. Photographs were taken at a range of scales and they contain a variety of land cover features as fine grain features, including road corridors and small lakes.

5. NED can generally be seen as an improvement over previous sources, in particular the DEM because it is a high resolution, seamless data source. Previous high resolution DEM data from the USGS were provided only over small areas with fixed boundaries. It was very time consuming to assemble these titles into a mosaic, when DEMs where required for large areas. Artifacts such as gaps or discontinuities were sometimes introduced at edges, and tiles were sometimes produced using different datums, projections or units. A seamless NED data set avoids these problems. Furthermore, NED is a progress in quality of slope, aspect, shaded-relief, and drainage information that may be derived from the elevation data.

Part 2:

2.

a.) Basemap and Hydrology are the names of the feature datasets in the geodatabase.

b.) NHDFlowline, NHDPoint, NHDWaterbody and Watersheds are the names of the feature classes in the hydrology dataset.

c.) NHDFlowline is a polyline layer. NHDPoint is a point layer. NHDWaterbody and Watersheds are both polygon layers.

3.

a.) topoq24.shp is a vector layer.

b.) The GIS Data format of topoq24.shp is a shapefile.

c.) Yes, there is metadata associated with topoq24.shp.

d.) The GIS Data format of NHDFlowline is the ArcGIS Geodatabase.

e.) Yes, there is metadata associated with NHDFlowline.

f.) Three examples of the keywords used to describe the NHDFlowline are: Hydrography, Stream and Lake.

g.) The NHDFlowline layer was created by: Earth Science Information Center, U.S. Geological Survey.4.

a.) Yes, there is still metadata associated with the layer (NHDFlowline.shp).

6.

b.) The USGS_QD-ID for Canoga park is 34118-B5.

7. The DOQQ is black and white.

8. Screenshot of CSUN campus



CSUN Campus

 10. Screenshot of expanded folder/file structure in ArcCatalog



12.

a.) The lacounty_lu01.shp layer has now a red exclamation point next to the grayed-out check box.

Lap #4 Working with Map Projections

Geog 206

Stefanie Wieschalla

Part 1: Map projections

Part 2: Significance of Map Projection

One might wonder why people need maps if a good globe can offer the most accurate representation of the earth. However, what is often forgotten is that a globe is actually not useful for many of the purposes for which we need maps. Map projections are necessary for creating maps thus maps could not exits without map projections. They permit us to represent some or the earth’s entire surface, at a large range of scales, on a flat, easily movable surface like for example, a sheet of paper. Map projections are more compact and easier to store, they can facilitate measuring properties of the terrain being mapped and they can show larger portions of the earth's surface at once. Besides that, they are cheaper to produce plus transport and they can further be applied to digital map data, which can be represented on a computer display. These useful traits of maps motivate the development of map projections. Today there are surely hundreds of different map projections to choose from. Each of them has its own strengths and corresponding weaknesses given that the process of transmitting information from the earth to a map causes every projection to distort at least somehow. Generally, distortion takes place in shape, area, distance and/or direction. Hence, every projection has its own advantages and disadvantages. There is simply no best projection because the appropriate projection for any given map depends on the scale of the map plus the function for which it will be utilized. For example, a projection could have intolerable distortions when used to map the entire United States, but may actually be a great alternative for a large-scale detailed map of California. Additionally, the properties of a map projection can also affect some of the design attributes of a map. Some projections are for instance clearly good for small areas, but some are not. It is also important to keep in mind that there are many ways to categorize the large variety of map projections. One of the most common classifications is by distortion characteristics. One need to question which properties of the earth does the projection maintain and which does it distort. A projection that maintains precise relative sizes is referred to as an equal area. Equal area projections are used for maps that indicate distributions or other occurrences where representing area accurately is significant. However, shape, distance and direction are distorted, especially when getting closer to the poles. Examples of the maps I used are the Gall Stereographic Projection and the Bonne Projection, which both indicate that the approximate distance between Washington, D.C. and Baghdad is about 5,970 miles. Now, a projection that preserves angular relationships and true shapes over small areas is called a conformal projection. These projections are generally utilized for navigational charts since angular relationships are important. Yet, distortion of area and direction increases away from the equator and is extreme in polar regions. Examples that I used for the assignment are the Mercator projection and the Eckert 1 projection. The estimated distance from Washington, D.C. to Baghdad varies in both examples. The Mercator projection approximates the distance to be about 8,389 miles, where the Eckert 1 projection indicates it only as 6,161 miles. The last two map projections that I choose where examples of equidistant projections, which maintain accurate distances from the center of the projection or along given lines. The projections are used for radio and seismic mapping and for navigation. However, shape, area and direction are, even though constant along any given parallel, quite distorted when the distance from the standard parallels increases. The examples I applied are the Equidistant Conic and the Equidistant Cylindrical projection. The estimated distance from Washington, D.C. to Baghdad varies in both examples again. Where the Cylindrical estimates to distance to be only 4,212 miles, the Conic indicates the distance to be around 6,277 miles. Initially, a map projection may also combine several of these characteristics or could be a compromise that distorts all the properties of shape, area, distance and direction within some tolerable limit. Even though not needed for the map exercise, a good example would be the Robinson projection, which is often used for world maps.

Part 3: Coordinate Systems & Projections Worksheet

1. An ellipsoid is a mathematical surface that is characterized by rotating an ellipse around its minor/polar axis. The ellipsoid estimates the surface of the earth without “topographic undulations”. The ellipsoid differs from a sphere given that it is slightly flattened at the poles.

2. The imaginary network of intersecting latitude and longitude lines on the earth’s surface is called a “Geographic Coordinate System”.

3. In contrast to the geographic North Pole that is located at the northern pole of the earth’s axis of rotation, the Magnetic North is the direction where a compass points to. It is important to realize that they are not at the same place at any point in time.

4. Datums are important because they tell one the latitudes and longitudes of a set of points on an ellipsoid, in order to determine surface locations. Datums are developed by determining a set of points by which all other latitudes and longitudes are established. One can determine these points through “geodetic surveys and monument points”.

5. A map projection is the alteration of coordinate positions from the earth’s curved surface onto a flat map. Points are “projected” from the earth surface and onto the map surface.

6. A developable (flat) surface is a geometric shape onto which the earth surface locations are projected. Common examples would be cones, cylinders, and planes.

7. d.) Lines of Latitude run north-south, converge at the poles, and mark angular distance east and west of the prime meridian.

8. a.) Clarke 1866 is now regarded as the best model of the earth for the region of North America.

9. For developing and analyzing spatial data when mapping countries or larger area it would be appropriate to use the Universal Transverse Mercator coordinate system given that it is a global coordinate system and it divides the earth into zones, which are each 60 degrees of longitude wide. Furthermore, the UTM zones have a large width that is necessary to accommodate large area analyses since all regions for an analysis are must be in the same coordinate system if they are to be analyzed together.

10. A great circle distance is a distance measured on the ellipsoid and in a plane through the earth’s center.

 

Lab #3: Data Formats & Models

Stefanie Wieschalla
Geog 206


1. A data model is a set of regulations utilized in order to illustrate and represent features of the “real world” in a computer. The two most frequently used data models are Geometric/Geospatial Data and Attribute Data models.

2. Topology is the analysis of geometric properties, which do not alter even when the forms are twisted, stretched or experience related geometric transformations. Furthermore, it confines and records the relationship between features. Hence topology is important because it is new and more efficient, especially regarding processing, then for example Spaghetti Models, which are often times prone to redundancy, unwanted overlap and/or inaccurate analyses.

3. The raster data model would definitely be best for representing hillside slope given that it provides a more accurate representation of continuous data. Hillside slopes are surely an example of continuous data because one can find them in many different regions of the world.

4. The relationship between spatial detail and cell dimension with regard to raster models is: the bigger the cell, the lower the resolution and the less detail one can resolve. Therefore, cell resolution relates to its size on the ground, where every grid cell holds one value, even if it is in fact empty.

5. The four types of attribute data are first nominal data, which is descriptive and/or categorical data as for example race/ethnicity, which can be divided between Caucasian, African-American, Asian, ect. Then there is ordinal data that is ranked/ordered like it is often times in surveys, where 1=Strongly disagree; 2=Disagree; 3=Neutral; 4=Agree; 5=Strongly agree. Third, there is the interval data, which is ordered, yet with absolute differences in magnitude and arbitrary zero. A good example would be temperature in degrees Fahrenheit. Lastly, there is ratio that is ordered data, with absolute differences in magnitude and absolute zero as for instance a person’s weight.

6. Two types of vector data file formats are: shapefile and coverages.

7. Two types of raster data file formats are: grids and images (tiff, jpeg, etc.).

8. One can do all of the following in ArcCatalog EXCEPT, c.) Select features.

9. Yes, the World.mdb geodatabase contains four feature classes.

10. The names of the feature classes that are contained in the World.mdb geodatabase are: cities, countries, disapp_ area and world30.

11. The flight_path.lyr layers file references spatial data.

12. One way to add data to ArcMap is to drag it from ArcCatalog. When the data is there, one can look at it as a map display and table of contents. The other way to add date to an ArcMap document, when ArcCatalog is not open, is to use the Add Data button in ArcMap, which is located on the Standard toolbar.

13. There are 699 records in the dissap_area feature class. One can determine this by looking at the Attributes category under the dissap_area feature class in ArcCataalog.

14.

Lab #2: ArcGIS & ArcMap

Stefanie Wieschalla
Geog 206



1.) There are four types of software products included in ArcGIS and these are Desktop GIS, Server GIS, Online GIS, ESRIData and Mobile GIS. Most of the time, in this course, we will be using Desktop GIS.

2.) It would be better to perform most of the data analysis and layer symbolization in data view because one can chose the “all-purpose view” for exploring, displaying and querying, but at the same time, one can focus on data in a single frame. However, the layout view serves simply for arranging map elements for printing and performing normal “data view” functions.

3.) There is first of all, the “What’s This” tool help that one can access by pressing Shift+F1 or to obtain further help, there is ArcGIS Desktop Help, which one can access by simply pushing the F1 button.

4.) Attributes are linked to geographic features in an attribute table via a unique identifier.

5.) When working in ArcMap, one uses a file called a “map document” or “mxd”.

6.) One way to zoom in/out on a map is by simply rolling the mouse wheel back and forth. The other way is to go to the toolbar and click on the zoom in or out tool and then click on a point you want to zoom in or out to.

7.) In the context menu of a layer, one can choose from a variety of different operations. One of them would be the “copy” option, where one can copy for instance a layer and then paste it somewhere else. Another example would be the “open attribute table” option, which consists of data associated with the geographic features or shapes. The last example, I want to point out is the “properties” selection, where one can change names and other features.

8.) If the check box next to a layer in the TOC is grayed-out, this means that the layer’s visibility depends on the map’s display scale. To resolve the issue, one would simply zoom in and then the layer will become visible.

9.) Small scale maps are actually characterizing large areas, like the entire world. The scale might be indicated as 1:400,000,000. In other words, large areas that are displayed in a map create small scale maps. Yet, large scale maps are representing a small area as for example the CSUN campus and could be illustrated by a scale of 1:100. Therefore, the larger the scale, the nearer features are to their original size.

10.) Features have shape and size and hence geographic objects have a huge selection of shapes. All of them can be represented as one of three geometrical forms, which are a polygon, a line or a point. A good example would be points that are generally used for cities and/or schools given that they are too small to be polygons, which would be countries or rivers. In contrast to for example countries, things as rainfall, elevation, slope, temperature and wind speed have no clear shape. Consequently, surfaces have measurable values for any specific location. The most well known surface is a raster, a matrix of identically sized square cells, where every cell stands for a unit of surface land and contains a measured or estimated value for that site.

11.) With GIS one cannot d) store project data.

12.) The minimum elevation value is 0 meters and can be found in New Orleans, USA. The maximum elevation value of the cities Earhart visited is 1045 meters and is located in Tucson, USA. I determined these values by clicking on the Identify tool on the Tools toolbar. When one clicks the tool, the Identify window opens. Then I went back to the map and clicked on the cities. The Identify windows show you the country and various other factors about a particular city as the elevation.

13.) The approximate distance from Dakar to Assab is 4,294.780241 miles, which I determined by clicking on the Measure tool on the Tools toolbar that opens the Measure window, which then gives you the opportunity to choose from the Units-drop-down arrow, point to Distance, to click on miles. Then I moved the mouse pointer over the city of Dakar, placed the crosshair and began to draw a line all the way to Assab. I ended the line by double clicking on it. The length of the line is now displayed in the Measure window. Another way of determining the approximate distance from Dakar to Assab, would be to open the attribute table of the Flight Path and then manually calculate the numbers that consists with the route that goes from Dakar to Assab.

14.) One way to figure out the names of cities shown on a map is to click on the Select Elements tool in the Tools toolbar and then move the cursor over the particular city you want to know the name of. The city’s name displays as a map tip. A different way would be to make the names of the cities visible at all times. One has to go to the Table of Contents, right click the layer that contains the cities and then click on label features. Now the name of each city appears next to the map feature.

15.)