Spatial Analysis using Vector Data # 2 Francisco Olivera, Ph.D., P.E. Srikanth Koka Department of Civil Engineering Texas A&M University

Buffers Creates a polygon graphic or a new polygon feature class in which the outlines are at a given distance from buffered graphics or features of a feature class Applies to one feature class only Select what you want to buffer (could be graphics or features of a feature class). Check the Use only selected features box if necessary.

Buffers Buffers can be created in three different ways: Single area at a given distance Single area at a distance defined in an attribute of the buffered features Multiple areas at distances multiple of a given value The window provides the opportunity to define the distance units.

Buffers Buffering polygons can intersect or be just the outline. Buffering polygons can be graphics, polygons appended to an existing polygon feature class, or a new polygon feature class.

Buffers Buffers allow one to identify which areas are within a certain distance from the buffered features. It can be used to identify optimal areas for building schools, residential areas, etc.

Joining Tables Joining tables consists of appending the attributes of a source table to a target table where the records are related through key fields in each table. The tables do not necessarily have to be attribute tables.

Joining Tables To join tables, right click on the target layer, then click Joins And Relates/Join and provide the information requested. Each record in the source table can be related to one or many records in the target table, but not vice-versa. This type of relation is called one-to-one or many-to-one (target-to- source). ArcGIS allows you to join tables under a one-to-many situation, but it will append the first of the many records in the source table that satisfy the relation. Joined tables are not modified. The tables will be joined only in the current project, but they can be used in their original format in other applications, including the current project itself.

Spatial Join Appends the attributes of a record of a source feature class to a record of a target feature class with which it shares the same location and creates a new feature class. Applies to two feature classes Spatially join two feature classes by right clicking on the target layer and then click Joins and Relates/Join. In the Join Data wizard, under the option that asks What do you want to join to this layer?, select Join data from another layer based on spatial location.

Spatial Join Spatially joining roads CClip (source) to rain gauges D (target) so that the nearest road is known for each rain gauge. Select the source feature class. Note that the target feature class is define when launching the Join data wizard. The word “closest" changes depending on the feature type of the target and source feature classes.

After spatially joining the source and target feature classes, a new feature class is created with attributes from the source being copied to the attribute table of the target feature class. The resulting feature class of rain gauges has attributes from the roads feature class, and also a new field “Distance” which is the distance of the rain gauge to the closest road. Spatial Join

The spatial relation between features of the target and source feature classes changes depending on their type.

Relating Tables In the case of a one-to-many relation, in which joining tables is not suggested as one of the many records will be randomly picked for the join, relating tables is an alternative solution. Relating tables consists of relating the records of a source table to the records of a target table through key fields defined for each of the two tables. When two tables are related, a record in the target table is selected, and Options/Relate Tables/Relate is clicked, the related record or records in the source table are automatically selected. Source Target

Relating Tables To join tables, right click on the target layer then click Joins and Relates/Relate. Related tables are not modified. The tables will be linked only in the current project; they may be used in their original format in other applications including the current project.

Attribute Statistics Statistics of the attributes of selected records for a given field are obtained by right clicking on the field header and then on the Statistics menu.

Summarizing Tables Summarizing tables consists of aggregating all the records that have the same value for a user-defined key field into a single record. The values of other fields are aggregated based on user-defined options. To summarize tables, click on the header of the key field of the table and then click on the Summarize button.

Summarizing Tables Summary tables are new tables in dbf, personal geodatabase table, or txt file format. The summarized table, however, has not been modified. A field called Count_Name contains the number of records in the original table that have been aggregated.