# UMES spatial join Discussion

Description

1) What is a spatial join?
2) What primary characteristic distinguishes a spatial join from an attribute join?

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GIS 580: GeoSpatial Intelligence & GIS
LECTURE 6:
Elementary GeoSpatial Analysis
The analysis of discrete entities
Professor, Dr. Sergei Andronikov
What the GIS is really all

The ANALYSIS SUBSYSTEM
GIS Spatial Analysis

1. The most enjoyable part of the GIS world.
2. The most powerful subsystem in the GIS.
3. The most abused one.
I need just a map !!!
GIS Spatial Analysis

Simple
Queries
Comparative
Analysis
Query
Combinations
Measurements
GIS Problems

1. To compare noncomparable nominal spatial
data with highly precise ratio spatial data.
2. Common belief: GIS is the panacea for ALL
locational problem solving.
FYI !!! GIS is an INCOMPLETE set of spatial
analytical tools.
YOU OBLIDGED to combine GIS tools with:
statistical analysis software;
mathematical modeling tools with computations;
BUT……

As a GIS Analyst you have to recognize the
GIS
potential capabilities
of +a GIS.
ULTIMATELY: the GIS should be able to
automate geography.
SPECIFICALLY: the GIS should be able to
automate most of the geographic analyses.
To enhance your knowledge you need to know
geographic analysis, statistical analysis,
systems modeling, and geostatistics.
GIS Data Query

In each digital database there are many different coverages
each containing a separate theme.
E.g trees. Point features
You are counting objects that occupy NO spatial dimension.
Lines are collection of grid cells that touch one another.
Polygons are groups of grid cells that are connected in much
the same way or share attribute values (REGIONS). You may
identify them by attribute.
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GIS Data Query

In vector you are displaying ALL points, and then
you will access the attribute database and its
tables.
Because they are linked to the entities, you are
able to selectively isolate specific types of point
objects.
Because explicit coordinates are used , you can
also obtain information about lines and polygons
by selecting them individually.
Locating & Identifying

Isolate, count, locate because it gives
an understanding of complexity of map
coverage.
Population density, # of houses,
plants,…
A quantitative measure of the amounts
will allow:
– to make analytical comparison.;
– to examine the relationships;
– to make further measurements and
comparisons (from absolute numbers to
relative: per area….)
Defining Spatial Characteristics
POINT OBJECTS

Like all entities point objects differ in locations, and
in attribute characteristics.
They can be separated by type, and by an ordinal
categorization.
If you classify point objects, you separate them by
value in interval or ratio scales as well as by type.
GIS must allow not only isolate, but to locate each
item individually for each class of data and
compare it with others of the same kind.
Isolate, select, quantify, locate point objects.
GIS not design to determine spatial relationship
LINE OBJECTS

Like point objects, LINES can be separated by
rankings or some measure.
BUT it can change in attribute type, rank or
magnitude along its overall length.
By using nodes to indicate the changes, we can
identify each segment as a separate entity.
Another attribute characteristic – a comparison what
falls on either side.
AREA OBJECTS

Can be defined, separated and retrieved on the basis of
category, class or magnitude.
1. The most useful – a measure of the SHAPES.
2. SIZE.
3. CONTIGUITY – a measure of the wholeness. How many
holes?
for animal habitats, fire hazards for forest regions
4. HOMOGENEITY of an area that is not necessarily defined
as a single polygon.
A measure of how much area is directly in contact with
polygonal features sharing the same attributes.
To group on some heterogeneous mix of attributes.
Isolate polygons with 12 or more trees as a diversity measure.
HIGHER LEVEL OBJECTS

POINTS
1. CENTROID – the point that occurs at the exact
geographic center of an area or polygon.
2. NODES – the points are significant as specific
locators along line and area entities.
LINE OBJECTS
1. BORDERS.
2. NETWORKS. A set of interconnected line entities
whose attributes share some common theme primarily
related to flow:
– straight lines (interstate highway);
– branching trees (a stream network);
– circuits (street patterns).
HIGHER LEVEL OBJECTS-2

AREA OBJECTS
REGIONS – areas that exemplify some unity of attributes.
Types based on spatial configuration:
1. Contiguous region. Wholly contained in a single polygon;
2. Fragmented region. Share some commonality of attributes.
3. Perforated region. Similarity of attributes, attribute mix.
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