ArcGIS is a collection of software products for building complete geographic information systems ( GIS ).
Unlike other versions of Environmental Systems Research Institute (ESRI) GIS software (e.g., ArcView 3.x), ArcGIS 8 and 9 provide an integrated GIS, combining object-oriented and traditional file-based data models with a set of tools to create and work with geographic data.
The ArcGIS software suite comprises the following three applications:
Because the earth is round and maps are flat, getting information from a curved surface to a flat one involves a mathematical formula called a map projection , or simply a projection.
This process of flattening the earth will cause distortions in one or more of the following spatial properties:
No projection can preserve all these properties; as a result, all flat maps are distorted to some degree. Fortunately, you can choose from many different map projections. Each is distinguished by its suitability for representing a particular portion and amount of the earth's surface and by its ability to preserve distance, area, shape, or direction. Some map projections minimize distortion in one property at the expense of another, while others strive to balance the overall distortion. As a mapmaker, you can decide which properties are most important and choose a projection that suits your needs.
South America in selected projections at identical scale.
Different Projections have different coordinates for same location.
From the above table its very clear that only coordinate information will not be sufficient to plot the points on the map. We need to have coordinate & the corresponding projection information to correctly plot the features on the map.
Right On the field in which the attribute to be updated.
Select Calculate Values
Field Calculator window appears, enter the data to be updated in field calculator. There are 3 major ways of calculating the attributes.
Calculate the attributes with a fixed value / data This will update all the records in the Statename field as “Punjab” Calculate the attributes with respect to the data available in other field In this the user has to select an existing field. In the above case the data available in TOWNCODE field will be updated in CODE field Calculate the attributes using functions This will update the values available DICTRICTNA field into Proper case
Some of the points to remember while calculating values
If any records are already selected in the attribute table, calculated data will be updated only to the selected records
If no records are selected in the attribute table, calculated data will be updated to all the records in the attribute table.
Other than SDE featureclass, records can be calculated without going into editing mode.
Before calculating, ensure that the right value is being calculated, records to be updated for selected records or all the records. Because you can’t undo the calculate values operation if the updation was done in non editing mode.
During calculate operation the operator must be aware on the data type of the field which is being updated i.e. the operator shouldn’t try to updated TEXT values in a numeric field or while updating a TEXT field the values must be given within a double quotes ( “ ” ).
ATTRIBUTE TABLE – CALCULATE VALUES, POINTS TO REMEMBER
Exercise : -
Create Fields and try updating attributes as show in the Slide “ ATTRIBUTE TABLE - PROPERTIES “
Calculate values using all the 3 types of updation.
FIELD BEING SUMMARIZED OUTPUT FILE HAVING THE SUMMERIZED RESULT DETAILS REQUIRED BY USER IN OUTPUT ON SELECTING THIS OPTION, DATA WILL BE SUMMARIZED FOR SELECTED RECORDS ONLY This option allows a table of summary information to be generated for the fields in the selected table. Unique values from a specified field are used as a basis for the summary information.
Exercise : - Given the Villages of Punjab with Census 2001 data. Generate a District wise report containing the details like Number of villages, Total Population in the District, Max & Min village population in that district, average village population.
Right On the field for which the statistics to be seen.
This can be performed on Numeric Fields only
A window containing the statistics of the selected field appears as shown below.
Statistics will provide, how many values the column has, as well as the sum, minimum, mean, maximum, and standard deviation of those values. A histogram is also provided showing how the column's values are distributed. Statistics are calculated for all numeric columns in the table.
Right On the Layers / Tables which is to be joined.
Select Joins & Relate Join
A Join data table window appears.
Joining involves appending fields (items) of one table to those of another through an attributes or field common to both tables. A join is usually used to attach more attributes to the attribute table of a geographic layer
Join Data Table appears
Select Join attribute from a table option.
Chose the common field in the Input file
Chose the Layer / Table to be joined
Chose the common field in the join file
Click on Advanced button
Select options like “Keep All Records” or “Keep Only Matching Records”
Type of outputs on selecting each option is shown below
Exercise : - Join attributes of Census 2001 data with Village locations