Transcript of Module 9 Working with XY Data. Overview Geographic Datums Working with Coordinates in ArcMap Go To...
- Slide 1
- Module 9 Working with XY Data
- Slide 2
- Overview Geographic Datums Working with Coordinates in ArcMap
Go To XY Transformations On the Fly Add XY Data
- Slide 3
- Geographic Datums Coordinates pairs, XY, are based on a
particular grid; a defined reference system In order to work with
coordinates, you need to know the Source reference system The
coordinates E-5 mean very little without knowing what map or page
in an atlas the E-5 references A Geographic Datum is a definition
for coordinates based on a particular calculation of the Earths
size and shape; it is a grid reference system of Latitude and
Longitude based on a specific model of the Earth, e.g. the GRS80
spheroid
- Slide 4
- Working with Datums in ArcMap Common Datums: WGS84 and NAD83
(and the older NAD27) Datums define spherical coordinates: Lat/Long
define locations on a specific 3D model of the Earth, or spheroid
It is imperative to know which spheroid or Datum your Latitude and
Longitude coordinates reference. Otherwise, its similar to having
the coordinates E-5 without knowing to which map the coordinates
refer
- Slide 5
- Geographic Coordinate Systems Latitude and Longitude represent
a Geographic Coordinate System or unprojected coordinates, i.e.
represent locations on the 3D model of the Earth Distances vary
between Degrees Longitude Ex. Longitude meridians converge at
poles; Distances between 1 Longitude much smaller in higher
latitudes than at the equator Because of this, you cannot calculate
Acres using a geographic coordinate system; the data must be
projected in order to calculate acres
- Slide 6
- Working with Datums in ArcMap Any number of projections may be
applied to these spherical coordinates in order to flatten the
Earth to two dimensions The same projection could be calculated
using different Datums: UTM projection based on NAD27 UTM
projection based on NAD83 UTM projection based on WGS84 Many other
projections and Datums!
- Slide 7
- Geographic Datums Why do we Care? Latitude and Longitude
coordinates are only part of the information You need to know what
Datum the lat/long coords reference in order to display them
correctly in ArcMap Sometimes you may need to convert lat/long
coordinates from one Datum to another, a process known as
Transformation See ESRI Help, Wikipedia, and other resources for
more info In general, consult your GIS Specialist before converting
data between Datums
- Slide 8
- Working with Datums in ArcMap The Web Soil Survey stores and
serves data in Geographic Coordinates based on WGS84. These are
Degrees, Minutes, Seconds or equivalent Decimal Degree units, not
projected Many other datasets may be received in WGS84 You wont
typically need to transform reference data to NAD83 for use in
ArcMap You should avoid data transformation unless you are sure you
know what you are doing You will need to set the transformation
method in the ArcMap so that datasets with different Datums will
display correctly using ArcMaps project on the fly
- Slide 9
- Transformations On the Fly When you add data to ArcMap that has
a different Datum than the Data Frame projection, you will receive
this warning. Click Transformations button
- Slide 10
- Verify the input Datums From the dropdown,
Select:WGS_1984_(ITRF00)_To_NAD_1983 Note: it doesnt matter whether
you are going from WGS84 to NAD83 or vice versa the SAME
transformation should be used Transformations On the Fly
- Slide 11
- Click OK Click Close Transformations On the Fly * This
transformation method will now be applied to all datasets added to
the data frame that have this source Datum
- Slide 12
- Working with Coordinates in ArcMap Typically work with Decimal
Degrees Latitude/Longitude (unprojected) West Longitude values must
be negative Must know Datum Convert Spreadsheet Coordinates to
desired Datum or Set ArcMap Data Frame projection/transformation
appropriately How to find specific locations or create data using
Coordinate data
- Slide 13
- Working with Coordinates in ArcMap Two main methods of working
with XY coordinates in ArcMap: 1. Go To XY. tool Finds XY locations
in a map Quickly locates one XY point at a time Not good for
locating multiple points End product is a graphic 2. Add XY Data
Adds a new map layer called an Event based on a table containing XY
coordinates Quickly locates numerous XY points at once Not
efficient for locating a single point Save Event layer out to
shapefile or feature class to make permanent
- Slide 14
- 1. Go To XY Click the XY icon from the main toolbar to open the
Go To XY tool Next click the dropdown and select the format of your
coordinates
- Slide 15
- Go To XY Copy/Paste or Type the coordinates Tip: X value is
Longitude Tip: Longitude must be negative for Western hemisphere
Click the Flash Button to see the location Note Options on the Go
To XY toolbar Here Ive clicked Add Point and Add Callout
- Slide 16
- Go To XY Here Ive added a point and callout for another set of
coordinates Note that each point and callout are graphics only You
may move the callouts without moving the point using the Select
Elements tool Ideal for quickly finding a location or adding quick
points and labels to a map
- Slide 17
- Go To XY To Save the point graphics as shapefile or feature
class: Select the points using the Select Elements tool
- Slide 18
- Go To XY Load the Drawing Toolbar if necessary Drawing dropdown
>> Convert Graphics to Features Navigate and Name the Output
dataset OK
- Slide 19
- 2. Add XY Data Why use add XY data method? Locate the
following: OSDs that have coordinates NASIS pedons that have
coordinates Hardcopy field notes and 232s that have coordinates
written on the form File >> Add Data >> Add XY
Data
- Slide 20
- 1.You must have coordinates 2.Create a table in Microsoft Excel
that has at least 2 columns All columns must have headers (no
spaces in header names) Add additional columns if necessary Enter
coordinates under appropriate X Y headers Step 1 Create a Table Add
XY Data XYSeries -102.93544.001Naff -103.15744.504Pilotbutte
-104.00144.105Cheney Required Columns Additional Column Coordinates
in this example are in Decimal Degrees ColumnHeaders* *NO spaces or
special characters!
- Slide 21
- Add XY Data Notes We recommend using Microsoft Excel since most
people are familiar with this program. You can use Microsoft
Access, Microsoft Excel, txt, and dbf files when creating your
tables. Be aware, some file types limit decimal places which may
affect your projections of XY data when working in decimal degrees,
which is another reason to use Excel. We recommend using X and Y
for your column headers, but you can name the columns whatever you
want as long as you dont have spaces and they dont exceed 10
characters. IMPORTANT: You can use either Latitude/Longitude or UTM
(Easting/Northing) coordinates in the table. X = Longitude and
Easting Y = Latitude and Northing
- Slide 22
- Add XY Data Notes cont IMPORTANT: Latitude and longitude data
must be in the form of decimal degrees for this tool to work and
the longitude data must have a negative sign in front of it. UTM
coordinates eastings are NOT negative and no sign is needed Data in
the form of degrees minutes seconds must be converted to decimal
degrees. The conversion formula is below: Example GPS point: 44
degrees, 27 min, 40 sec 96 degrees, 47 min, 28 sec Latitude in DD =
(44 + (27/60) + (40/3600)) = 44.46111 Longitude in DD = (-96 +
(47/60) + (28/3600)) = -96.79111 Notice the negative sign in front
of the longitude data
- Slide 23
- Add XY Data File >> Add Data >> Add XY Data Browse
to table If using Excel file, select the Sheet name Select: X for X
field Y for Y field Select Edit to choose coordinate system if
necessary Click Ok to run Step 2 Run ADD XY Tool
- Slide 24
- Add XY Data A new layer will be added to your table of contents
and the points will display in ArcMap. The points displayed are in
an Event layer and are temporary. They may be saved in the Map
Document (.mxd) To make permanent: Right click on the layer (event)
Data >> Export Data Export to shapefile or geodatabase
- Slide 25
- Exercise Become familiar with Go To XY tool Calculate
Coordinate values for Existing Points Use Add XY Data tool to
create new points
- Slide 26
- Open Module 9 >> XY_data.mxd Click XY tool Double-click
Module 9 >> Lat_Longs.txt to open in Notepad This text file
contains the coordinates for two points Set the Units to Decimal
Degrees using the dropdown Copy/Paste the coordinates into the Go
To XY tool Add Points and labels for each location ( ) Select both
Points using the Select Elements tool Add the Drawing Toolbar if
necessary Drawing dropdown >> Convert Graphics to Features
(use data frame projection) Navigate to the Module 9 directory and
save the points as TwoPoints.shp Add them to your map Delete the
graphics so that you only have the point shapefile based on these
coords >> Save. NOTE: You must add POINTs and not simple
Call-out labels in order to convert to points Go To XY
- Slide 27
- Open the table for the TwoPoints.shp created in the last step.
The shapefile includes a Name field that contains the original
coordinates used in the XY tool Calculate Point Coordinates What
DATUM do these coordinates represent? Are they WGS84, NAD27,
NAD83?
- Slide 28
- ANSWER: We added the coordinates to a data frame with a spatial
reference UTM zone 14 NAD83. ArcMap located the coordinates based
on this spatial reference; that is, using the XY tool, we
essentially said, Show me where these latitude/longitude
coordinates are in UTM zone 14 NAD83 and then we converted those
graphics to points. The original coordinates were thus displayed as
NAD83 coordinates We exported the points out to a shapefile using
the Data Frame coordinate system, so the resulting TwoPoints
shapefile is projected to UTM zone 14 NAD83 Now well calculate
THREE different sets of coordinates for those same two points:
Geographic (lat/long) NAD83 UTM zone 14 (NAD83) Geographic
(lat/long) WGS84 First, well add the necessary fields to the
TwoPoints.shp table: Open the TwoPoints.shp table if necessary
Table >> Add Field
- Slide 29
- Name the field: X_n83 Type: Text Length: 25 characters OK Name
the field: Y_n83 Type: Text Length: 25 characters OK Repeat these
steps to add another field for the Y value: RESULT:
- Slide 30
- Name the field: X_utm Type: Text Length: 25 characters OK Name
the field: Y_utm Type: Text Length: 25 characters OK Now repeat
these steps to add fields to hold the UTM coordinates: RESULT:
- Slide 31
- Name the field: X_wgs84 Type: Text Length: 25 characters OK
Name the field: Y_wgs84 Type: Text Length: 25 characters OK Now
complete these steps a third time adding fields for WGS84
coordinates: RESULT:
- Slide 32
- Right-click on the X_n83 field >> Calculate Geometry
>> X Coordinate of Point Use the coord system from data
source i.e. the shapefiles projection, not the data frame Select
Decimal Degrees for units OK
- Slide 33
- Result: X values match the original coordinates from the.txt
file that was used to generate the points The labels also match the
original values but have been rounded to 9 decimal places (the
labels have been rounded, but the actual coordinates have not been
we just calculated the actual coordinates and they match the
original values)
- Slide 34
- Now Calculate the Y Coordinate Right-click on the Y_n83 field
>> Calculate Geometry >> Y Coordinate of Point Use the
coord system from data source i.e. the shapefiles projection, not
the data frame Select Decimal Degrees for units OK
- Slide 35
- Result: Y values match the original coordinates from the.txt
file that was used to generate the points The labels also match the
original values but have been rounded to 9 decimal places (the
labels have been rounded, but the actual coordinates have not been
we just calculated the actual coordinates and they match the
original values)
- Slide 36
- Now well calculate UTM Coordinates Right-click on the X_utm
field >> Calculate Geometry >> X Coordinate of Point
Use the coord system from data source i.e. the shapefiles
projection, not the data frame Select Meters for units OK
- Slide 37
- Repeat for Y UTM Coordinates Right-click on the Y_utm field
>> Calculate Geometry >> Y Coordinate of Point Use the
coord system from data source i.e. the shapefiles projection, not
the data frame Select Meters for units OK
- Slide 38
- We now have both lat/long and UTM coordinates for the two
points Next well calculate where these two points are referencing a
different Geographic Datum: WGS84
- Slide 39
- Right-click on Layers >> PropertiesSelect the Coordinate
System tab and collapse all the folder to match the graphic
- Slide 40
- Expand the Geographic folder Expand the World folder Select WGS
1984 Do not click OK yet.
- Slide 41
- Verify that WGS_1984 is Selected Click the Transformation
button Select the WGS_1984 (ITRF00) to NAD_1983 Transformation from
the list (probably first option) Click OK
- Slide 42
- The Data Frame coordinate system is now in Geographic, WGS84
The data layers are un-projected and appear squarer Calculate Point
Coordinates
- Slide 43
- Open TwoPoints table if necessary Right-click on X_wgs84
>> Calculate Geometry Calculate the X coordinate Select the
Data Frame coordinate system Select Decimal Degrees
- Slide 44
- Right-click on Y_wgs84 >> Calculate Geometry Calculate
the Y coordinate Select the Data Frame coordinate system Select
Decimal Degrees
- Slide 45
- We now have three sets of coordinates calculated for the same
two points: The source coordinate system for the TwoPoints
shapefile is UTM 14 NAD83 We calculated the lat/long coordinates
based NAD83 (the source coordinate system) We calculated the UTM
coordinates based on UTM 14 NAD83 We calculated the lat/long
coordinates based on the WGS 1984 Datum by changing the Data Frame
coordinate system, setting the appropriate Transformation method,
and calculating the points using the Data Frame coordinate system
instead of the TwoPoints source coordinate system In the resulting
table we can see the differences between NAD83 and WGS84
coordinates This is why when you have coordinates it is imperative
to know the original source, i.e. Datum they reference
- Slide 46
- Exercise Become familiar with Go To XY tool Calculate
Coordinate values for Existing Points Use Add XY Data tool to
create new points
- Slide 47
- If you have a large number of coordinates it is impractical to
copy/paste them into the Go To XY tool one at a time as
demonstrated in the last step Instead, use the Add XY Data tool to
Display coordinates in a spreadsheet lat/long coordinates as
Decimal Degrees The coordinates are NAD83 coordinates Optionally
Export these points to a Geodatabase or shapefile
- Slide 48
- Set the Data Frame Coordinate System to match the coordinates
in the spreadsheet, i.e. NAD83 Open the Data Frame Properties
Right-click on Layers >> Properties >> Coordinate
System Tab >> Geographic Coordinate Systems folder >>
North America >> Select NAD_1983 Click OK The coordinates are
NAD83 lat/long The ArcMap data frame was set to WGS84 in the
previous step and we need to reset it to NAD83 Otherwise, ArcMap
will locate the coordinates as if they were WGS84 coordinates!
- Slide 49
- Add XY Data Now well add the coordinate values from the
spreadsheet as Events File >> Add Data >> Add XY
Data
- Slide 50
- Add XY Data >> Navigate to the Excel spreadsheet called
coords.xlsx in the Module 9 directory >> Double-click on the
file and select the coords$ Worksheet (You must select a specific
Worksheet; often it will be the default name Sheet1 in the list)
>> Add
- Slide 51
- Add XY Data The fields in the spreadsheet are named X and Y
ArcMap attempts to auto-populate the X and Y fields but you should
always verify this is correct NOTES: Field headers can be named
anything but with No Spaces No Special Characters And the
coordinate values must be either numeric or General data type
Verify and click OK
- Slide 52
- Add XY Data The Events layer is added to the Table of Contents
as coords$.Events Now that weve verified that they show up
correctly well save them out to the geodatabase
- Slide 53
- Add XY Data Right-Click on the Events layer >> Data
>> Export Data
- Slide 54
- Add XY Data Change the Type to File and Personal Geodatabase
feature classes Navigate Module 9\NE159.gdb\FDS_NE159\ Name the new
feature class myNewPts Save Yes, Add the new layer to the Map
- Slide 55
- Add XY Data Now a little clean-up: R-click and Remove the
Events layer Change the symbol for the ne159_p layer to the big
green dot. Turn on the ne159_p layer
- Slide 56
- Add XY Data The coordinates in the spreadsheet were derived
from the ne159_p data layer and should match
- Slide 57
- Exercise Summary Use the Go To XY tool to locate one or a few
points Optionally save the graphic points using the Drawing toolbar
>> Convert Graphics to Features Use Calculate Geometry to
retrieve XY coordinates for Point datasets Optionally change the
data frame projection to retrieve different coordinate values, i.e.
projected versus geographic Use Add XY Data to display a
spreadsheet of coordinates called Events in ArcMap Once you verify
that they appear in the correct location, optionally save as a
permanent data layer Remember to select the ITRF00 transformation
when displaying data in WGS84 and NAD83 at the same time. Do not
convert data between datums without consulting your GIS
Specialist.
- Slide 58
- Bonus Question: What if you have a spreadsheet of WGS84
coordinates and you want to display them with your NAD83 data?