Geographical Information System

(CEL747)

Tutorial 1 & 2

SURYAKANT

M.Tech 2nd

semester

Water Resources Engineering

2014CEW2110

Department of Civil Engineering

IIT Delhi -110016

TUTORIAL 1

ARC CATALOG

1. What is the function of each of the following buttons?

Ans. Large Icons, List, Details, Thumbnails, Launch Arc Map,

Show/Hide Arc Toolbox Window, Show/Hide Command Window, Start

Model builder, What’s This?

2. How many individual files comprise the "IndiaPoi" shapefile?

Ans. The ‘indiapoi’ contains seven supporting files as follows:

IndiaPoi.dbf IndiaPoi.prj IndiaPoi.sbn IndiaPoi.sbx IndiaPoi.shp IndiaPoi.shp.xml

IndiaPoi.shx

3. “state" is seen as a folder in Windows Explorer. View “state"

in ArcCatalog, what specific format of geospatial data is it? Does this

data appear as a folder or a single file in Arc Catalog?

Ans. After view “state” in ArcCatalog it appears as single file with

“coverage” format and it contains four types of feature classes as arc,

label, polygon, tic. These data doesn’t appear like folder there are four

types of Arc feature classes as shown below.

4. What specific type of GIS data is the file "India"? Does this appear

as one single file in Windows Explorer or a folder?

Ans. It appears as “India.mdb” file. It refers to personal Geodatabase file.

It is a single file not a folder.

5. When you preview Geography which icons become active

in ArcCatalog?

Ans. When I preview Geography in ArcCatalog there are eight icons are

active, those are Zoom In/Out, Pan, Full Extent, Go back to previous

Extent, Go to next Extent , Identity, Create thumbnail.

6. In the Preview of Dam, what is the latitude longitude

of Sardar Sarovar Dam? This is shown in the lower right corner

of ArcCatalog. Give answer in Degrees, Minutes and Seconds.

Ans. Sardar Sarovar Dam Lat 21 49’ 49” N, Long 73 44’ 50” E

Metadata

7. Why do you think the fields are automatically filled in ISO 19139

Metadata Implementation Specification style?

Ans. Since, it is the standard format for representation of the data as

specified by ISO so it is also followed in India and hence, the fields are

automatically filled in ISO 19139 Metadata Implementation Specification

style.

8. What is the "Horizontal coordinate system" (Datum) of these data?

Ans.

Horizontal coordinate system i.e. XY Coordinate System is

WGS_1984_UTM_Zone_43N.

Arc Toolbox

9. Use the toolbox Search to find all the tools related to "overlay"

operations. List the top three tools along with a brief description (in your

own words) of their functions.

Ans.

Erase: It will Creates a feature class by overlaying the Input Features

with the help of polygons of the Erase Features.

Identity: It can be used for geometric intersection of the Input Features

and Identity Features.

Intersect: It is used for geometric intersection of the Input Features.

ArcMap

10. What information is provided in the symbology tab when we select

the Mediam Description field? From this window, how can we change the

data representation?

Ans.

11. Where else do you think the transparency function might be (more)

useful?

Ans: It is used in GIS for legends and graphics but it can be used in

PowerPoint also.

12. How would you remove duplicate labels?

13. In which state is the Rihand Dam? Write the query that you have used

for determining the answer.

Ans. Rihand Dam is a concrete gravity dam located in Pipri, Sonbhadra

District of Uttar Pradesh, India. Rihand dam has length of 934.21 m. The

maximum height of the dam is 91.44 m and was constructed during

period 1954-62.

TUTORIAL 2

TOPOLOGY

1. What are the topology rules available to find out errors for a polygon

feature class?

Ans: In the ArcGIS data model, polygons can be coplanar, they can overlap,

they can be discontinuous, or they can contain nested islands and lakes. To

avoid these errors following rules are available:

Must Not Overlap: This rule requires that the interior of polygons in

the feature class not overlap. The polygons can share edges or

vertices. This rule is used when an area cannot belong to two or more

polygons.

Must Not Have Gaps: This rule requires that polygons not have voids

within themselves or between adjacent polygons. Polygons can share

edges, vertices, or interior areas. Polygons can also be completely

disconnected. This rule is used when polygons or blocks of

contiguous polygons should not have empty spaces within them.

Must Not Overlap With: This rule requires that the interior of

polygons in one feature class must not overlap with the interior of

polygons in another feature class. Polygons of the two feature classes

can share edges or vertices or be completely disjointed. This rule is

used when an area cannot belong to two separate feature classes.

Must Be Covered by Feature Class of: This rule requires that a

polygon in one feature class must share all of its area with polygons

in another feature class. This rule is used when an area of one type,

such as a state, should be completely covered by areas of another

type, such as counties.

Must Cover Each Other: This rule requires that the polygons of one

feature class must share all of their area with the polygons of another

feature class. Polygons may share edges or vertices. Any area defined

in either feature class that is not shared with the other is an error. This

rule is used when two systems of classification are used for the same

geographic area and any given point defined in one system must also

be defined in the other.

Must Be Covered By: This rule requires that polygons of one feature

class must be contained within polygons of another feature class.

Polygons may share edges or vertices. Any area defined in the

contained feature class must be covered by an area in the covering

feature class. This rule is used when area features of a given type

must be located within features of another type.

Boundary Must Be Covered By: This rule requires that boundaries of

polygon features must be covered by lines in another features class.

This rule is used when area features need to have line features that

mark the boundaries of the areas.

Area Boundary Must Be Covered by Boundary of: This rule requires

that boundaries of polygon features in one feature class be covered by

boundaries of polygon features in another feature class. This is useful

when polygon features in one feature class, such as subdivisions, are

composed of multiple polygons in another class, such as parcels, and

the shared boundaries must be aligned.

Contains Point: This rule requires that a polygon in one feature class

contain at least one point from another feature class. Points must be

within the polygon, not on the boundary. This is useful when every

polygon should have at least one associated point, such as when

parcels must have an address point.

2. Which topology rule you will use to remove overshoot & undershoot

errors.

Ans: A common topological error with polyline features is that they do not

meet perfectly at a point (node). This type of error is called an undershoot if

a gap exists between the lines, and an overshoot if a line ends beyond the

line it should connect to.

Figure Topology Errors 1:

The result of overshoot and undershoot errors are so-called ‘dangling

nodes’ at the end of the lines.The result of overshoot and undershoot

errors are so-called ‘dangling nodes’ at the end of the lines. The

following rule can be applied to overcome the above mentioned errors:

Must Not Have Dangles: This rule requires that a line feature must touch

lines from the same feature class at both endpoints. An endpoint that is

not connected to another line is called a dangle. This rule is used when

line features must form closed loops, such as when they are defining the

boundaries of polygon features. It may also be used in cases where lines

typically connect to other lines, as with streets. In this case, exceptions

can be used where the rule is occasionally violated, as with cul-de-sac or

dead end street segments.

3. What are the rules available to find out errors for a line feature class?

Ans: A well-designed geodatabase will have only those topology rules

that define key spatial relationships needed by an organization.

Must Not Overlap: This rule requires that lines not overlap with

lines in the same feature class. This rule is used where line

segments should not be duplicated; for example, in a stream feature

class

Must Not Intersect: This rule requires that line features from the

same feature class not cross or overlap each other. Lines can share

endpoints.

Must Not Have Dangles: This rule requires that a line feature must

touch lines from the same feature class at both endpoints. An

endpoint that is not connected to another line is called a dangle.

Must Not Have Pseudo-Nodes: This rule requires that a line

connect to at least two other lines at each endpoint. Lines that

connect to one other line (or to themselves) are said to have

pseudo-nodes.

Must Not Intersect Or Touch Interior: This rule requires that a line

in one feature class must only touch other lines of the same feature

class at endpoints. Any line segment in which features overlap, or

any intersection not at an endpoint, is an error.

Must Not Overlap With: This rule requires that a line from one

feature class not overlap with line features in another feature class.

This rule is used when line features cannot share the same space.

For example, roads must not overlap with railroads or depression

subtypes of contour lines cannot overlap with other contour lines.

Must Be Covered By Feature Class Of: This rule requires that lines

from one feature class must be covered by the lines in another

feature class.

Must Be Covered By Boundary Of: This rule requires that lines be

covered by the boundaries of area features. This is useful for

modeling lines, such as lot lines, that must coincide with the edge

of polygon features, such as lots.

Endpoint Must Be Covered By: This rule requires that the

endpoints of line features must be covered by point features in

another feature class.

Must Not Self Overlap: This rule requires that line features not

overlap themselves. They can cross or touch themselves, but must

not have coincident segments.

Must Not Self Intersect: This rule requires that line features not

cross or overlap themselves. This rule is useful for lines, such as

contour lines, that cannot cross themselves.

Must Be Single Part: This rule requires that lines must have only

one part. This rule is useful where line features, such as highways,

may not have multiple parts.

4. Built topology between stream and Roads. Now list the rules which

could be used to set relation among them.

Ans:

A topology can be created in ArcCatalog by right-clicking on the data set

name and selecting New -> Topology from the context menu.

A wizard appears to guide the user through the creation of topology.

Then following steps are click next on the first page of wizard to move to

second page, on second page set the name of the topology i.e. stream or

roads and specify the tolerance then click next, on third page specify the

feature class that will participate in the topology and then click next, on

fourth page specify ranking of each feature class within the topology then

click next, on fifth page define integrity rules and click next, on sixth page

i.e. summary page that will lists all the choices made in the wizard.

5. What is the function of the rule “Must Not Have Pseudos”?

Ans: A line must connect to at least two other lines at each endpoint. Lines

that connect to one other line (or to themselves) are said to have pseudo

nodes. The basic function of the rule “Must Not Have Pseudos” is; when

line features must form closed loops, such as when they define the

boundaries of polygons or when line features logically must connect to two

other line features at each end, as with segments in a stream network, with

exceptions being marked for the originating ends of first-order streams.

6. What do you mean by cluster tolerance?

Ans: The minimum tolerated distance between vertices in a topology.

Vertices that fall within the set cluster tolerance are snapped together during

the topology validation process. [ESRI software].The cluster tolerance is the

distance range in which all vertices and boundaries in a shape file or feature

dataset are considered identical or coincident.

7. If two polygons are overlapping, how will you remove this error?

Ans: The possible solution of this kind of problem is as:

Subtract: The Subtract fix removes the overlapping portion of

geometry from each feature that is causing the error and leaves a gap

or void in its place. This fix can be applied to one or more selected

Must Not Overlap errors.

Merge: The Merge fix adds the portion of overlap from one feature

and subtracts it from the others that are violating the rule. You need to

pick the feature that receives the portion of overlap using the Merge

dialog box. This fix can be applied to one Must Not Overlap error

only.

Create Feature: The Create Feature fix creates a new polygon feature

out of the error shape and removes the portion of overlap from each

of the features, causing the error to create a planar representation of

the feature geometry. This fix can be applied to one or more selected

Must Not Overlap errors.

8. What is the need to provide Rank to features in Topology? Why do we

carry out validation in topology?

Ans: The Rank allotment in topology is important to manage the relative

accuracy between the all participating feature class. The x,y and z–ranks

represent the accuracies of the feature class relative to other feature classes

participating in the topology. Feature classes with a higher rank, such as 1

are more accurate than feature classes with a lower rank, such as 2. Ranks

are a relative measure of accuracy; the difference between two features

classes of ranks 1 and 2 is the same as two feature classes with ranks of 1 &

50.

Validation in topology: Once the topology has been created with all the

feature classes and rules, you can optionally choose to validate the

topology. However, this is not required, since the entire topology is covered

by a dirty area. Until the topology is validated, the topological relationships

of the features cannot be guaranteed.

9. Why we need to define Domain in a Geodatabase. Can we do even

without domain? Is it possible to give same Domain to many feature

classes?

Ans: A domain is a declaration of acceptable attribute values .Attribute

domains are rules that describe the legal values of a field type, providing a

method for enforcing data integrity. Attribute domains are used to constrain

the values allowed in any particular attribute for a table or feature class..

Whenever a domain is associated with an attribute field, only the values

within that domain are valid for the field. In other words, the field will not

accept a value that is not in that domain.

Yes it is possible to give same Domain to many feature classes because

domains are created for the entire geodatabase, not just for a specific feature

class or feature dataset. Same domains can be used by any feature class

within the geodatabase.