# CS代考程序代写 data structure SPATIAL MAPS

SPATIAL MAPS

STA465: Theory and Methods for Complex Spatial Data

Instructor: Dr. Vianey Leos Barajas

WORKING WITH SPATIAL DATA STRUCTURES IN R

We’ll exclusively use R to work with spatial data:

➤

➤

There are two books we will use to learn how to work with spatial data structures and plot spatial data in R:

Geocomputation with R

Geospatial Health Data: Modeling and Visualization with R-INLA and Shiny

Spatial data structures: Beyond plotting points

Data sets will now have additional structures https://r-spatial.github.io/sf/reference/index.html

➤ ➤

➤

➤

➤ ➤

GEOCOMPUTATION WITH R

PDF of book: https://geocompr.robinlovelace.net

R PACKAGES

install.packages(“sf ”): a class system for geographic vector data install.packages(“raster”)

install.packages(“spData”) remotes::install_github(“Nowosad/spDataLarge”)

library(“sp”)

What about ggplot2 or base R?

For spatial data structures, we need to go beyond that We can use it in combination with ‘sf ’ or ‘sp’ structures

– –

VECTOR DATA

SIMPLE FEATURES (SF)

Figure from ‘geocomputation with R’

From https://r-spatial.github.io/sf/articles/sf1.html

## library(spData) plot(world)

## library(spData) world

plot(world[“pop”])

SPATIAL DATA

How is the data structured here?

plot(world[“pop”])

➤

ASIA

R CODE:

R CODE:

RASTER DATA

RASTER DATA

Consists of a raster header and matrix — whose rows and columns represent equally spaced cells (aka pixels)

Raster maps usually represent continuous phenomena such as elevation, population density or spectral data

Can represent discrete features such as soil or land-cover classes with the help of a raster data model

➤

➤

➤

RASTER DATA

The cell of one raster layer can only hold a single value:

CONTINUOUS AND CATEGORICAL RASTERS

WHAT CAN WE DO?

Given a coordinate, we can: Identify elevation

➤

➤

➤

Connect to land cover type

DATA STRUCTURE IN R

COORDINATE REFERENCE SYSTEM (CRS)

3D AND 2D EARTH SURFACES

From ‘geospatial health data’

GEOGRAPHIC COORDINATE SYSTEMS

A geographic coordinate system specifies locations on the Earth’s three-dimensional using latitude and longitude values.

PROJECTED COORDINATE SYSTEMS

Map projections are transformation of the Earth’s three- dimensional surface as a flat two-dimensional plane

All map projections distort the Earth’s surface in some fashion. Can only preserve one to two of the following:

Area

Direction

Shape

Distance properties

➤

➤

➤ ➤ ➤ ➤

PROJECTION TYPES

Conic — projected onto a cone along a single line of tangency or two lines of tangency

Best suited for maps of mid-latitude areas Cylindrical — maps the surface onto a cylinder

Most often used for plotting the world

➤

➤

➤

➤

Planar — projects data onto a flat surface touching the globe at a point or along a line of tangency

Typically used in mapping polar regions

➤

➤

FIGURE 6.2: Mollweide projection of the world.

FIGURE 6.3: Winkel tripel projection of the world.

PROJECTED COORDINATE SYSTEMS

Universal Transverse Mercator — UTM Preserves local angles and shapes.

Divides Earth into 60 zones of 6 degrees of longitude in width

Each zone uses transverse Mercator projection to map a region of

➤

➤

➤

Position on Earth given by UTM zone number, hemisphere, and easting/northing coordinates in zone (measured in meters)

Eastings are referenced from the central meridian of each zone, and northings are referenced from the equator. The easting at the central meridian of each zone is defined to have a value of 500,000 meters

➤

➤

➤

BACK TO PREVIOUS DATA SET:

CRS OPTIONS

CRS

Specifies how coordinates are related to locations on Earth

CRS is either geographic or projected

In R, CRS specified using `proj4` strings that specify:

Projection Ellipsoid Datum

➤ ➤ ➤

➤ ➤ ➤

SELECTING AND SETTING CRS

Depending on the data set you work with, it may already have a defined CRS — typically comes as a `shape` file (.shp)

➤

What if it doesn’t?

There will be choices to be made!

Don’t make an assumption without thoroughly contacting people who know the data best

➤

➤

➤

https://www.spatialreference.org

There are a some commonly used CRS, for example:

WGS84/4326

➤

➤

➤

SETTING AND CHANGING A CRS

SETTING AND CHANGING A CRS

SETTING AND CHANGING A CRS

SETTING AND CHANGING A CRS

MANIPULATING SPATIAL DATA STRUCTURES

COMBINING/MODIFYING SPATIAL DATA STRUCTURES

You want to combine two data sets — but they have different CRS…

You have two data sets, one with points and one with multipolygons — how do you combine them?

Overlaying multipolygons, strings, points

Computing distances, areas from spatial data structure!

➤

➤

➤

➤