lab 3: exploring data structures overviewesa.snre.umich.edu/classes/gis777/lab03.pdf · lab 3:...

Lab 3: Exploring Data Structures

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Overview:

This lab will explore the data structures used to implement the two most common GIS spatial data

models: vector and raster. These data models define how the data are created, stored, manipulated,

and displayed. In this lab you will explore how ArcGIS deals with data in each of these models.

In addition, you will become familiar with common formats used for storage, and how to exchange

and import geographical data.

The vector data model (points, lines, and polygons) can be stored in several different file formats.

In ArcGIS, the common file formats are coverages, shapefiles, and geodatabases.

Coverages are native to ESRI’s original Arc/Info software, and are still sometimes used in

contemporary GIS applications. Coverage information is stored in a topologically structured

manner (you will work with topology in a future lab). Topology is explicitly encoded information

about the spatial connections between features. By encoding spatial relationships in this way, the

data structure provides a means to query and analyze the data for information about adjacency and

contiguity without calculating the connections each time an analysis is performed. The geographic

and attribute portions of coverages are stored separately and linked together via database relations

that are managed with relational tables stored in an INFO directory.

ESRI’s help system provides a great deal of illustrated introductory information about coverages

and other file formats. For coverages, look in the ArcGIS Desktop Help system under the Contents

tab, check Geodata │Data Types │ Coverages |What is a coverage? For an illustrated description

of topology, see Geodata │Data Types │ Topologies │ Topology in ArcGIS.

Shapefiles are the native data format of ArcView 3.x GIS, which was created as a user-friendly but

less analytically powerful, supplement to ArcInfo. They are similar to coverages in that the

geographic and attribute portions are stored separately (geography in the SHP file and attributes

in the DBF file) and linked together by information stored in the SHX file. They are different from

coverages because the spatial or geographic elements are stored as individual objects with no

explicit representation of adjacency and contiguity built into the data structure (i.e. there is no

topology information). Therefore, if topology-based analyses are required, the software needs to

calculate spatial relationships on-the-fly (depending on the size of the dataset, this can be very

cumbersome).

You can find more information regarding shapefiles in the Help system. Check Geodata │Data

Types │ Shapefiles │ What is a shapefile? & Shapefile file extensions. Also, check Geodata │Data

Types │ Tables │ A quick tour of tables and attribute information & Tabular data sources for

diagrams and further explanation.

Geodatabases are the contemporary data structures for ESRI products, and are native to ArcGIS.

Therefore, they will be the primary focus of vector data development throughout the remainder of

the semester. They are similar to both coverages and shapefiles, in that topological structuring is

possible (like coverages) and geographic elements are stored as individual objects (like shapefiles).

They are unique from coverages and shapefiles in several ways:

Unlike coverages, in which topology is automatically defined by the system, topology in

geodatabases is user defined by selecting and applying (i.e., validating) topology from a

suite of rules that specify the desired spatial relationships.


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Geodatabases can have ‘behaviors’ detailed within the data structure to better model real-

world relationships.

There are two types of geodatabases freely available to all Arc users, Personal geodatabases and

File geodatabases. File geodatabase are more current and exhibit several advantages over personal

geodatabases, so we will be using them for the remainder of our labs. Some of these advantages

are as follows:

In Personal geodatabases, all data (both geographic and attribute) can be stored in a single

MDB file (derived from the Microsoft Access database engine). As such, they are tied to

the Windows operating system. File geodatabases are native to ArcGIS and stored as a file

system folder. They are compatible across platforms.

The maximum size of a Personal geodatabase file is 2GB; however, the effective size is

between 250 to 500 MB as performance slows after that. File geodatabases can hold up to

1 TB of data per dataset (each File can store many datasets), and have significantly faster

performance than any data formats we have discussed thus far.

It is worth noting that Geodatabases created in ArcGIS 10.x, cannot be open or edited in earlier

ArcGIS versions. Geodatabases created in ArcGIS 9.x can be opened and edited in ArcGIS 10.x.

Look in the Help system under Geodata │Geodatabases │ Managing Geodatabases │ An

overview of the geodatabase │ A quick tour of the geodatabase & Essential readings about the

geodatabase for further explanation.

GRID is the native ESRI format to store data using the raster data model. The grid format is a

typical example of a raster data structure, in that it stores a matrix of cells that are organized into

rows and columns. Each cell is assigned a single value to represent categories or numerical

attributes at each location. The Spatial Analyst extension in ArcGIS offers several tools for

manipulation and computation of data that are stored as raster data models. ArcGIS has the ability

to display many other types of non-native raster data, including Imagine files (.img), American

Standard Code for Information Interchange or ASCII (.asc), Tiff (.tif) and Joint Photographic

Experts Group or JPEG (.jpg). To see the complete list, check Geodata │Data Types │ Rasters

and images │ Supported raster data. In addition, check the section Fundamentals of raster data.

Learning Objectives:

To explore and understand data structures used by ArcGIS

To gain an introduction to the various topology options

To comprehend the various raster display options and how they affect your data

To learn to join tables

To identify the parameters that define a raster data set

To become familiar with some tools for importing data.

To be submitted:

(20 pts) A write-up answering the questions throughout the lab. Graphics may be used to help

illustrate your answers. (500 words maximum).

http://help.arcgis.com/en/arcgisdesktop/10.0/help/009t/009t0000000q000000.htm


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Procedure:

1. The ArcCatalog graphical interface

The latest version of ArcGIS can access all the data structures listed on the previous page, plus a

number of other structures that are not native to ESRI software. These include a number of

databases, tables, and image formats. ArcCatalog is an object-oriented interface that displays each

data type using icons similar to those seen below.

Question 1. (1 point) For each of the icons displayed below, use your notes and ArcCatalog

interactions with real data to determine what it represents. You need to correctly identify the data

type and (where applicable) geometry for full credit (e.g., is geodatabase line feature class) –

**These icons are in color and color matters.

A E

B F

C G

D H

2. Coverage structure

The coverage structure consists of information stored in a system defined in a topologically

structured manner (i.e., the data structure has explicitly encoded information about the spatial

relationships between features). The geographic and attribute portions of coverages are stored

separately and linked together via database relations that are managed with relational tables stored

in the INFO directory. Although typically constructed to represent a single geographic feature

type (points, lines, or polygons), the coverage can store multiple feature classes within itself. The

various features within the coverage are part of a hierarchy constructed to represent the single

feature type (i.e., points define the endpoints of arcs, arcs define the boundaries of polygons, and

polygons are the feature type of interest). In this section, you will explore the various levels of the

coverage within ArcCatalog and Windows Explorer.

Within ArcCatalog, connect to your “Lab03_data” directory and observe the files with it.

Note what three coverages are available for your use (you should have a few coverages

composed of various feature types).

Explore the various coverages by clicking on the pluses (+) and minuses (-) next to the file

names or by double clicking on the file names.

Use the Preview tab to explore both geography and table (right-click on feature class and

open Item Description if using ArcCatalog via ArcMap).

To change between geography and table view, use the pull-down option at the bottom of

ArcCatalog within the Preview Tab:


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In the Geography view, use the geography tools to explore the

various feature classes within the coverages. For example, the arc feature class consists

of lines (e.g., roads, rivers, or polygon boundaries); the point or label feature class consists

of many points for locations (e.g., cities or study sites) or polygon attribute labels; the

polygon feature class contains the geographic extent of all polygons (e.g., lakes or states);

and the tic feature class contains the definition of geographic positioning or extent of the

coverage.

Now open Windows Explorer, navigate to your lab directory (i.e. GSS777/Lab03_data)

and look for the various coverages. Windows Explorer sees a Coverage as a folder because

it stores files within itself. You will notice the individual files (arc data files) stored within

the various coverages. These files are representative of the various feature classes (arc, aat

– arcs, pat/nat – points or nodes, pal – polygon

attributes, tic – geographic tics, etc.).

The ‘INFO directory’ (or folder called “info”),

is created automatically and is required in any

workspace that contains coverages. The info

directory contains the information needed to track

and link the relationships between the various arc

data files. An example of this linking process is

seen in Figure 1. It shows how the arc attribute

table, which contains the descriptive information

about the roads, is related to the node attribute

table, which contains the coordinates of the nodes

(road intersections).

**Note: The ‘info directory’ is the ‘director’ of the various components of your

coverage. Without it, your coverage would be invalid and therefore, non-useable. A

single info folder can store the information of several different coverages. For this

reason, it is very important to use only ArcCatalog or another Arc/Info utility when

copying or deleting coverages. ArcCatalog has the ability to maintain the

relationships in the ‘info directory’ when copying files.

Figure 1: Coverage structure You will not actually see this image; this just gives

you an idea of what is going on behind the scenes.


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One way to transport coverage structures is to compress them. The

format is a single Interchange File that has the extension *.e00. The

interchange file format is not exclusive to coverages - it can also be used to

compress grids and tin files. The ArcToolbox offers options to decompress

e00 files (Conversion tools │ To Coverage │ Import from E00).

3. Shapefile Structure

The shapefile structure is much simpler than either the geodatabase or coverage. Each shapefile

consists of one feature class represented by a set of related files and does not use topological

structuring. Data storage is limited to simple geographic and attribute information. While a

shapefile may contain up to seven related files, the three of most importance are the .dbf, .shp,

and .shx. Respectively, these files store the data’s attribute information, geographic information,

and internal relational tables linking the geographic and attribute information. In this section, you

will explore the shapefile structure within ArcCatalog and Windows Explorer. For the full list of

shapefile file extensions, please refer to Professional Library │Geodata │Data Types │Shapefiles

│Shapefile file extensions.

Within ArcCatalog, navigate to your working directory and the location of the three Chelsea

shapefiles (chel_roads.shp, chel_places.shp and chel_landuse.shp, remember what the icons

mean from above).

Explore the various shapefiles – you should notice that selecting the shapefile itself does not

reveal additional feature classes, as it does in a coverage. As stated above, one shapefile = one

feature class, even though it takes several different files to create a single shapefile.

Be sure to use the preview tab for both the geography and table options to explore your data –

notice again that a set of navigation tools has become active for you to investigate your

different data sets.

Now open Windows Explorer, navigate to your lab directory and look for the various files that

compose the shapefile. The individual files that comprise an individual shapefile will share the

same name with different extensions (e.g., chel_roads.shp, chel_roads.shx, and chel_roads.dbf,

etc).

3.1. Creating a point shapefile from tabular data

Tabular data containing X/Y point locations can be easily transformed into point shapefiles (or

other formats, for that matter). Check the file gas_stations.txt; the file contains a geographic

location (X and Y columns) as well as a label or attribute for each set of coordinates:

“Type”, “X”, “Y” Header

"Gas and diesel", 251372.4, 4690292.0 Values

"Gas", 250095.5, 4691953.7 Values

Note that values must be separated by commas, and quotation marks are required to define

text values.

To create a shapefile from a text file with X/Y locations:


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Open ArcMap and add the table gas_stations.txt (remember the Add Data tool ).

Notice that the Table of Contents mode changes from List By Drawing Order to List

By Source .

In the Table of Contents, listed by source, right-click on the table

and from the new menu select the option Open to display the

table. Review the table so you understand what you’re adding.

Right-click again on the table and select

“Display XY Data;” this option allows

you to display X/Y coordinates as a map

layer.

A new window will open. Automatically the fields X/Y will be

recognized (*Note, in case the software is not able to identify the

X/Y fields automatically, the user can manually select the correct

X/Y columns). Click OK. If you encounter a warning, click OK.

A temporary map layer will be displayed as an event (e.g. “gas_stat.txt.Event”).

To save your file permanently as a point shapefile, right-click the point map file you just

created in the Table of Contents; select the option Data │ Export Data.

In the new window, select the option “this layer’s source data” [even though the coordinate

system is unknown for this file, it is still good practice]. Click on the to select your

working directory. A new window will open.

Provide a proper name; use something that reflects the data content. Avoid long names

with more than 13 characters; do not leave spaces between words (e.g. NO gas stat.shp /

YES to gas_stat.shp). In the option “Save as type” select Shapefile. Select “Save.” You

will return to the previous window. To finish the process click OK.

A window will appear asking if you would like to add the exported data to the map as a

layer. Say Yes to display the file.


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Microsoft Excel tables can also be used in ArcGIS. Excel tables can added directly into ArcMap

in the same way you did with the text file. If there is more than one worksheet in the file, the user

needs to browse the Excel file and select the worksheet they would like to open. In ArcGIS, the

first row of a worksheet will be used as the table header. Some of the naming recommendations

for the first-row fields are:

Field names must start with a letter.

Field names must contain only letters, numbers, and underscores.

Field names must not exceed 64 characters.

ArcMap can only read 255 characters per cell. Fields have to be consistent, all numeric; all text

or all date:

For more information related to the use of Microsoft Excel files, please refer to Geodata │ Data

Types │ Tables │ Creating and editing tables │ Using Microsoft Excel and Access files.

3.2. Joining Tables

The join function in ArcGIS allows you to join two tables together based on a shared attribute:

(ESRI, 2015)

This is particularly useful for importing data from a table that does not include the spatial features.

For instance, if you have a table of demographic data for each US State and a shapefile of US

states, where both datasets contain the state abbreviation (MI, CO, NH etc.), you can import the

demographic data as a table into ArcGIS and join it with the US State shapefile based on the state

abbreviation. Then, you will be able to view/analyze your demographic data spatially.

To join tables:

Add MI_counties.shp to ArcMap using the Add Data tool. This is your target layer. This

is a shapefile of all the counties in MI, downloaded from the Michigan Geographic Data

Library.

Add the (non-spatial) table titled “Census_Data.xls” to ArcMap as well, and note that you

add the specific Excel sheet (MI_Data$) rather than the entire file. This is your join table.


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It contains population statistics downloaded from the US Census

(https://www.census.gov/popest/data/counties/totals/2013/CO-EST2013-alldata.html)

Open each file’s corresponding table by right clicking on the layer in the Table of Contents

and selecting “View Attribute Table.” Can you see which attribute (column) is shared

between the two datasets? In MI_counties.shp, you’ll see that each county has a specific

FIPS code listed in the FIPSNUM column. In the Census_Data.xls table, you’ll see the

same numbering scheme in the COUNTYFIPS column. Note that both datasets also contain

county names. This is useful for determining that the FIPS numbers actually match, though

generally it is best to complete joins on the least complex shared attribute, as there is less

chance for an error.

To join the two datasets, right click on your target

layer (MI_Counties.shp), select Joins and Relates |

Join… This pops up a window in which you indicate the

shared attribute between the two files. Using the

dropdown menus, select “FIPSNUM” as the field in this

layer that the join will be

based on. Be sure that the

table you’re joining to the

layer is set as MI_Data$ and choose COUNTYFIPS as the

field in the table to base the join on. Leave the default join

option (keep all records), click “OK”.

Re-open the attribute table of MI_Counties.shp and notice that

all the columns from MI_Data$ have been added to this

attribute table.

Using the Properties | Symbology tab, explore the newly

joined data by changing the county data from a single symbol

to separate categories. Look in your Lab 3 folder for

information on what the various attributes are.

NOTE: if you want your join to be permanent, right click on

MI_Counties in your Table of Contents, Click Data | Export

Data, keep the defaults, but specify where you want your layer to be saved.

NOTE: if you’re planning to use an Excel table, be sure to save it as a .xls table and NOT

a .xlsx table. ArcGIS has difficulty reading the newer version of excel tables.

For more information and the difference between one-to-one and many-to-one joins visit

http://resources.arcgis.com/en/help/main/10.2/index.html#//005s0000002n000000

4. Geodatabase Structure

The geodatabase structure is object-oriented and hierarchical. It consists of the root of the

geodatabase itself (workspace), possibly many feature datasets (containers for data with similar

topologies – similar but not identical to a coverage), and the individual feature classes (the actual

points, lines, and polygons) representing different data sets. With the exception of some raster

formats, all forms of data (both geographic and attribute) can be stored in a single MDB file.

To incorporate integrity and consistency into data editing procedures, topology is user defined.

The user selects from a suite of topology rules that specify the desired spatial relationships,

subtypes (hierarchy of data), default attribute values, and attribute domains (coded selection list

for attribute editing), which can be encoded directly into the data structure. Additionally,

https://www.census.gov/popest/data/counties/totals/2013/CO-EST2013-alldata.html


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geodatabases can have ‘behaviors’ detailed within the data structure to better model the real world

relationships that the data symbolize. In this section you will explore the hierarchy of the

geodatabase within ArcCatalog and Windows Explorer.

Within ArcCatalog, navigate to your working directory and the location of the Lab3_File

geodatabase. Explore the various personal geodatabase feature classes found within the

chelsea_data feature dataset

Be sure to use the Preview tab for both the

geography and table options to explore your

data.

Now open Windows Explorer, navigate to your

Lab3 directory and look for the various feature

classes and attribute tables within the geodatabase. How does Explorer store .gdb files? (Note:

A file with a .lock extension will appear if you have opened a geodatabase in ArcCatalog or

ArcMap. It indicates that the file is “locked” and cannot be modified by another user until the

current use is complete, at which time the .ldb file will disappear.)

Question 2 (4 points): How are Shapefiles, Coverages and Geodatabases represented/organized

in Windows Explorer? What does this difference say about the similarities and differences in the

structure of these vector data models?

Also, one advantage of vector files is their ability to store information for multiple attributes; can

you think of cases where that is useful (list 3 examples)?

5. Grid Structure

An ArcGIS GRID is a raster data structure that follows the typical raster data model in that every

location is represented by a cell with a single attribute value. The cell values are typically numbers

that represent data such as land cover, elevation, and temperature. In this part of the lab, you will

explore the structure of several rasters.

First, add a new data frame to our current project. A data frame is

like a “page” where you display your map layers. ArcMap allows

you to have several data frames in a project. You will add a new data

frame from the menu Insert and select Data Frame. A new frame

will be added to the Table of Contents, notice that the Table of

Contents is empty, meaning there are no map layers displayed (if you

wish to return to the first frame, just right-click on it and from the

menu select Activate). For more information about frames, refer to

Using data frames in ArcGIS 10 Help.

In your new frame, add the layer chelland1_30m GRID. Although raster data is generally

described as a “field view” or “continuous surface”, these data are still considered discrete (do

you understand why?).


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Right-click on the chelland1_30m file in the table of contents and select Properties…

Choose the Display tab

In the “Resample during display using” option box, notice the Nearest Neighbor option is the

default for discrete data (i.e., nominal categories are typically stored as integers) – this will

display the true pixel value assigned to each cell when changing the zoom.

Click OK to exit out of the properties window.

Zoom in to a fairly large scale on the map display (until the pixelation in the data is obvious),

then go back into properties and change the resample during display using (as in the previous

step) to bilinear interpolation or cubic convolution, notice what happens to the display of

the land cover categories.

Question 3 (2 points): What happened visually to the way the land-cover categories were

represented on the screen when you switched the resample method from the nearest-neighbor

default to bilinear interpolation or cubic convolution? Are the bilinear interpolation and cubic

convolution methods appropriate ways of displaying the land cover data on the screen? Why or

why not? Think in terms of discrete vs. continuous data.

Make sure to switch back to nearest neighbor resampling.

5.1. From ASCII grid to Raster

A common format to store raster data is as an ASCII grid text format. Go to Lab03_data folder in

Windows Explorer and open the file dem30m_chel.txt. The first six rows are a “header”; they


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describe the properties of the grid. After the header, cell values are listed separated by a single

space as showed in the example below:

ncols 233 number of columns

nrows 281 number of rows

xllcorner 658545.3068164 lower left corner X coordinate value or minimal X value

yllcorner 196975.22526095 lower left corner Y coordinate value or minimal Y value

cellsize 30 size of the pixel or cell

NODATA_value -9999 value given to cell with No data or absence of data.

940.481 951.4073 955.019 957.6366 950.3968

953.4296 954.6925 956.4779 957.9591 959.9766

To convert an ASCII grid to a GRID file, in ArcCatalog:

Click on the ArcToolbox Icon A new window will be displayed

Expand the Conversion Tools option (click on the plus sign). From the new list click on To

Raster and select ASCII to Raster.

In the ASCII to Raster window, add the dem30m_chel.txt as the Input ASCII raster

file. On the Output raster option, click on the icon to select your working directory.

Name the output file as cheldem_30m. In the Output data type option, select INTEGER.

When finished, the new GRID will be displayed in the frame.

Right-click on the cheldem_30m file in the table of contents, select Zoom to Layer. Make

sure the chelland1_30m layer is unchecked here so you can actually see cheldem_30m, or

move cheldem_30m to the top of the list in the Table of Contents.

Again, right-click on the cheldem_30m file in the table of contents, select Properties…

Choose the Display tab, as above notice the “Resample during display” using option

selects nearest neighbor as the default (be thinking about why this may be inappropriate

in this case).

Click ok, and return to the map display.

Cell or pixel values


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The values recorded in a digital elevation model (DEM) are an example of continuous data. That

is, the values of the thing being measured change smoothly from one location to the next. There

are no natural “steps” in the data. Because of this, continuous data are typically measured in real

numbers. However, they can be stored using integers to make the files smaller or to reflect a

precision of measurement that is no finer than whole numbered units. Zooming in on such a grid,

you will see that at the boundaries of grid cells, the values jump from the value stored in one cell

to the value stored in the neighboring cell. By taking advantage of the continuous nature of the

data, ArcMap provides the option of interpolating the values so that these jumps are not so

apparent.

Set the scale of your frame as 1:1,500 . Come back to the

Properties…/ Display window and change the resample during display using option to

"bilinear interpolation." Note how the display is changed - think about whether or not this

is appropriate for the elevation data.

Question 4 (2 points): What happened to the representation of the DEM data on the screen when

you switched the resample method to bilinear interpolation from nearest neighbor? Why is this

method more or less appropriate for displaying elevation data than for landcover data?

5.2. Multispectral images

A multi-band raster is a raster data set can display up to three distinct bands of data at one time.

Each of the bands may represent a different wavelength of energy (visible to microwave) and are

‘loaded’ into one of the additive color display options of red, green, or blue (RGB). The

arrangement of these bands within the RGB options is dictated by the user’s needs and what the

user would like to enhance in the image (e.g. some band combinations enhance visualization of

vegetation, or water quality). For color infrared (CIR) imagery (which is provided here), the color

red is normally used to display near-infrared (NIR) energy. This leaves green and red energy to be

represented in the image by the colors blue and green, respectively. To explore ArcMap’s ability

to use multi-band rasters, you have been provided with a color infrared image from the Michigan

Center for Geographic Information (MCGI).

Add chelsea_ne.sid image to your ArcMap display

Notice that bands one, two, and three (spectral designations by MCGI) are loaded into the

red, green, and blue color options respectively.

Alter the combinations of bands one, two, and three with the RGB color options and see

the effect it has on the display. To accomplish this, right-click on the chelsea_ne.sid file

in the table of contents, select Properties.., select the Symbology tab, change the

combination, select OK – view the results of your choices in ArcMap.


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Something to think about: Do any of your altered band/color combinations assist you in

identifying different kinds of features on the ground?

5.3. Finding specific X/Y locations

The following section will guide you through finding a specific location based on X/Y values, for

example the three sets of coordinates listed below:

661869, 201321 662116, 201292

662039, 201100

To approximately find the above X/Y locations, first zoom the data out to the full extent,

then move the mouse around the window and observe the X/Y coordinates reported in the

lower right corner of the ArcMap screen. Once you’ve roughly found the desired location,

center it in the screen using the pan controls, and zoom to a scale at 1:1500. This should

center you relatively close to the desired area. At this scale it should be fairly easy to move

your “identify tool” cursor around to exactly locate the specific coordinates. If the

fractional scale option is grayed-out, you will need to define the units for your data view –

to do so, right click on Layers in the Table of Contents, select Properties, and then General

tab, and set the Map and Display units to Meters.

To precisely find the location, you can also use the “Go To XY” tool located in the “Tools”

toolbar.

Set up units to meters. Click on the Go to XY tool and a new small window will display.

On this new window, click on the black down arrow (last icon on the right). A new menu

will display, select Meters


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Type the first coordinate (661869, 201321) and hit Enter. You will see that the location is

going to flash with a green dot on the screen. You can use the Add point tool to draw

the XY location. Also, you can draw the point with a label with its coordinates with the

tool Add Labeled Point tool .

Repeat the same procedure for the other two coordinates

Question 5 (3.5 points). Using the available tools in ArcMap, determine the pixel values for

each of the three grids on display: chelland1_30m, cheldem_30m and chelsea_ne.sid and fill

in the table below. Make sure you are zoomed in far enough to be very accurate!

Location

Land

Pixel

Value

Land

Use

(CLASS)

DEM

Stretched

value

DEM

Elevation

(Pixel

Value)

Multi-Band Pixel

Values

R G B

661869, 201321

662039, 201100

662116, 201292

5.4. Exploring raster structures

The underlying structure of any raster data file is important to know because it defines the

characteristics of the grid. Parameters include resolution, number of bands present, minimum, and

maximum values you could find and the geographic extent of your data to name only a few. These

properties can be explored by using ArcCatalog.

From the ArcCatalog table of contents, right-click on chelland1_30m and select

Properties… – from here you will be able to explore the parameters of the raster. Do the

same for cheldem_30m, and chelsea_ne.sid.


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Question 6 (2.5 points). You should be able to find, for example, information for the files like

that listed in the table below. Complete the table and include it in your write-up as you answer to

Question 6.

Parameter chelland1_30m cheldem_30m chelsea_ne.sid.

Number of Rows

Number of Columns

‘x’ Cell Size

‘y’ Cell Size

Format

Source Type

Number of Bands

Question 7 (5 points): Going back to the research question you outlined in Q1 of Lab1, what are

the file extensions of the 5 layers you have identified and what data model do they correspond to?

If you already know from your data search that a given layer exists and is available in a particular

format, explain why you think the data provider chose that format for the data. If you cannot find

existing data for some of the 5 layers, explain what format you think they should be in and why.

(Note: almost all data can be stored in either structure, but almost all data is more appropriately

stored in one or the other). Also, in cases where you feel the data should be stored in vector

structure, which of the three types (coverage, shapefile, or geodatabase) is most appropriate? Why

(think about complexity of the data structure, topology, etc.) --End Lab 3

lab 3: exploring data structures overviewesa.snre.umich.edu/classes/gis777/lab03.pdf · lab 3:...

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