Misaligned and improperly referenced data can be a common source of error that can cause major data and map interpretation mistakes. To avoid these errors, it is important to ensure that all the layers used are in the same projection. It is especially important when larger areas are being considered because the difference in shape (angles), distance, direction and the resulting distortion is amplified as a larger area is covered – leading to larger discrepancies in interpretation.

ArcMap tools like Project-on-the-fly can only change the coordinate system to align layers in the map while keeping the coordinate set intact e.g. if the layers are created using different scales. Whereas, other tools like projecting a layer using the ArcCatalogue will address the discrepancy in coordinate values as well. It will transform the coordinate set itself and create a new version of the original dataset to perform the action required e.g. to match the spatial reference system of all the layers in the map. Not only this helps to bring all the layers in the same projection to align shapes and angles, but also align the very coordinates to ensure accurate representation. Therefore, Project-on-the-fly can be used if a very large scale area is being focused upon. However, in a much smaller scale map, it is critical to ensure that both the projection and coordinates are adjusted to align together.

 

THE PROJECTED COORDINATE SYSTEM CAN BE CHANGED BY THE FOLLOWING STEP:

Look at your image to determine projection/check whether the projection matches the rest of the layers:

go to the layer properties > Source > scroll down to read the details of the image.

 

THE PROJECTION CAN BE CHANGED BY CLICKING:

data frame properties > Coordinate System> Projected Coordinate Systems > Continental > … pick the area corresponding to your image location > …pick coordinate system that matches

 

DEFINING YOUR PROJECTION: (important when the data being used is not properly documented and is inappropriately referenced)

For a layer that you want to add to your map but the data it contains is missing the spatial reference that will allow it to align itself with the rest of the layers/data :

Make sure your projected coordinate system matches that of the rest of the layers.

  1. Launch ArcCatalog from within ArcMap, and dock the Catalog window to the right edge of ArcMap.
  2. Find the layer you want to add to the map and Properties > XY Coordinate system tab. You’ll notice the coordinate system is ‘unknown’.
  3. Look at the Feature Extent tab and notice the magnitude of Max/Min values for the X and Y coordinates.
  4. Add the nat_parks layer to the map. A warning pops up stating that the spatial reference is missing. Click Ok. The layer is added to the Table of Contents
  5. If you cannot your layer – zoom to layer.

 

TO MAKE SURE THE COORDINATE SYSTEMS ARE ALIGNED, TOO:

  1. Remove the misaligned layer from the Table of Contents.
  2. In the Catalog tab, navigate to the same layer and launch the its properties
  3. Under the XY Coordinate System tab click on Geographic Coordinate Systems > pick the area corresponding to your image location > …pick coordinate system that matches and click OK.
  4. Add the layer back to the map

 

TO PROJECT THE LAYER:

  1. From the tool toolbar launch ArcToolbox and dock the window that appears to the right edge of ArcMap.
  2. In ArcToolbox, navigate to Data Management Tools > Projections and Transformations > Project
  3. In the tool’s dialog window enter the following parameters: enter in the Input Dataset: [the layer you want to project]
    (The program reads the current coordinate system and fills the next box) and enter in the Output Dataset: [location where you want to save the projected payer in your computer]
  1. Output Coordinate System: Click on browse button and select Projected Coordinate Systems > Continental > pick the area that corresponds to your layer > pick the desired projection
  2. Click Ok. A progress window will appear and after a few seconds the operation will be completed.
  3. Add the new layer to the map.

 

It is important to preview your data with ArcCatalog, check whether the layers have coordinate system information and look for the common/official projections for the study area. Some regions may also have recommended or official coordinate systems to be used for analysis. It is crucial to ensure that all the layers are in the same projection to allow for smooth calculations and analysis.

 

REMOTE SENSING FOR GIS ANALYSIS

Many exploration techniques e.g. geothermal energy resource exploration or geographic analysis techniques, although are very reliable and accurate, do not cover a lot of ground, the sites are irregularly spaced and are expensive. Remote sensing is a powerful and highly cost effective way to do geographic analysis while filling in these data gaps and allowing for access to imagery and data across spatial and temporal scales.