diff --git a/src/main/java/com/seibel/lod/core/enums/config/DistanceGenerationMode.java b/src/main/java/com/seibel/lod/core/enums/config/DistanceGenerationMode.java
index 712de3cc3..20e2b93e8 100644
--- a/src/main/java/com/seibel/lod/core/enums/config/DistanceGenerationMode.java
+++ b/src/main/java/com/seibel/lod/core/enums/config/DistanceGenerationMode.java
@@ -19,6 +19,8 @@
 
 package com.seibel.lod.core.enums.config;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * NONE <br>
  * BIOME_ONLY <br>
@@ -92,4 +94,46 @@ public enum DistanceGenerationMode
 	{
 		this.complexity = complexity;
 	}
+	
+	// Note: return null if out of range
+	@Nullable
+	public static DistanceGenerationMode previous(DistanceGenerationMode mode) {
+		switch (mode) {
+		case FULL:
+			return DistanceGenerationMode.FEATURES;
+		case FEATURES:
+			return DistanceGenerationMode.SURFACE;
+		case SURFACE:
+			return DistanceGenerationMode.BIOME_ONLY_SIMULATE_HEIGHT;
+		case BIOME_ONLY_SIMULATE_HEIGHT:
+			return DistanceGenerationMode.BIOME_ONLY;
+		case BIOME_ONLY:
+			return DistanceGenerationMode.NONE;
+		case NONE:
+			return null;
+		default:
+			return null;
+		}
+	}
+	
+	// Note: return null if out of range
+	@Nullable
+	public static DistanceGenerationMode next(DistanceGenerationMode mode) {
+		switch (mode) {
+		case FULL:
+			return null;
+		case FEATURES:
+			return DistanceGenerationMode.FULL;
+		case SURFACE:
+			return DistanceGenerationMode.FEATURES;
+		case BIOME_ONLY_SIMULATE_HEIGHT:
+			return DistanceGenerationMode.SURFACE;
+		case BIOME_ONLY:
+			return DistanceGenerationMode.BIOME_ONLY_SIMULATE_HEIGHT;
+		case NONE:
+			return DistanceGenerationMode.BIOME_ONLY;
+		default:
+			return null;
+		}
+	}
 }
diff --git a/src/main/java/com/seibel/lod/core/enums/config/VerticalQuality.java b/src/main/java/com/seibel/lod/core/enums/config/VerticalQuality.java
index 9d82f9486..494f78620 100644
--- a/src/main/java/com/seibel/lod/core/enums/config/VerticalQuality.java
+++ b/src/main/java/com/seibel/lod/core/enums/config/VerticalQuality.java
@@ -19,6 +19,8 @@
 
 package com.seibel.lod.core.enums.config;
 
+import org.jetbrains.annotations.Nullable;
+
 /**
  * heightmap <br>
  * multi_lod <br>
@@ -77,4 +79,34 @@ public enum VerticalQuality
 	{
 		this.maxVerticalData = maxVerticalData;
 	}
+	
+	// Note: return null if out of range
+	@Nullable
+	public static VerticalQuality previous(VerticalQuality mode) {
+		switch (mode) {
+		case HIGH:
+			return VerticalQuality.MEDIUM;
+		case MEDIUM:
+			return VerticalQuality.LOW;
+		case LOW:
+			return null;
+		default:
+			return null;
+		}
+	}
+
+	// Note: return null if out of range
+	@Nullable
+	public static VerticalQuality next(VerticalQuality mode) {
+		switch (mode) {
+		case HIGH:
+			return null;
+		case MEDIUM:
+			return VerticalQuality.HIGH;
+		case LOW:
+			return VerticalQuality.MEDIUM;
+		default:
+			return null;
+		}
+	}
 }
\ No newline at end of file
diff --git a/src/main/java/com/seibel/lod/core/handlers/LodDimensionFileHandler.java b/src/main/java/com/seibel/lod/core/handlers/LodDimensionFileHandler.java
index 3c1362425..0f0297906 100644
--- a/src/main/java/com/seibel/lod/core/handlers/LodDimensionFileHandler.java
+++ b/src/main/java/com/seibel/lod/core/handlers/LodDimensionFileHandler.java
@@ -29,6 +29,7 @@ import java.util.concurrent.Executors;
 
 import org.apache.commons.compress.compressors.xz.XZCompressorInputStream;
 import org.apache.commons.compress.compressors.xz.XZCompressorOutputStream;
+import org.jetbrains.annotations.Nullable;
 
 import com.seibel.lod.core.api.ClientApi;
 import com.seibel.lod.core.enums.config.DistanceGenerationMode;
@@ -100,6 +101,8 @@ public class LodDimensionFileHandler
 	
 	
 	
+	
+	
 	//================//
 	// read from file //
 	//================//
@@ -116,125 +119,65 @@ public class LodDimensionFileHandler
 		
 		for (byte tempDetailLevel = LodUtil.REGION_DETAIL_LEVEL; tempDetailLevel >= detailLevel; tempDetailLevel--)
 		{
-			String fileName = getFileNameAndPathForRegion(regionX, regionZ, generationMode, tempDetailLevel, verticalQuality);
+			File file = getBestMatchingRegionFile(tempDetailLevel, regionX, regionZ, generationMode, verticalQuality);
+			if (file == null) continue; // Failed to find the file for this detail level. continue and try next one
 			
-			try
+			long fileSize = file.length();
+			if (fileSize == 0) continue; // file is empty. Let's not try parsing empty files
+			try (XZCompressorInputStream inputStream = new XZCompressorInputStream(new FileInputStream(file)))
 			{
-				// if the fileName was null that means the folder is inaccessible
-				// for some reason
-				if (fileName == null)
-					throw new IllegalArgumentException("Unable to read region [" + regionX + ", " + regionZ + "] file, no fileName.");
+				int fileVersion;
+				fileVersion = inputStream.read();
 				
-				File file = new File(fileName);
-				if (!file.exists())
+				// check if this file can be read by this file handler
+				if (fileVersion < 6)
 				{
-					//there is no file for current gen mode
-					//search others above current from the most to the least detailed
-					VerticalQuality tempVerticalQuality = VerticalQuality.HIGH;
-					do {
-						DistanceGenerationMode tempGenMode = DistanceGenerationMode.FULL;
-						do {
-							fileName = getFileNameAndPathForRegion(regionX, regionZ, tempGenMode, tempDetailLevel, verticalQuality);
-							if (fileName != null)
-							{
-								file = new File(fileName);
-								if (file.exists())
-									break;
-							}
-							//decrease gen mode
-							if (tempGenMode == DistanceGenerationMode.FULL)
-								tempGenMode = DistanceGenerationMode.FEATURES;
-							else if (tempGenMode == DistanceGenerationMode.FEATURES)
-								tempGenMode = DistanceGenerationMode.SURFACE;
-							else if (tempGenMode == DistanceGenerationMode.SURFACE)
-								tempGenMode = DistanceGenerationMode.BIOME_ONLY_SIMULATE_HEIGHT;
-							else if (tempGenMode == DistanceGenerationMode.BIOME_ONLY_SIMULATE_HEIGHT)
-								tempGenMode = DistanceGenerationMode.BIOME_ONLY;
-							else if (tempGenMode == DistanceGenerationMode.BIOME_ONLY)
-								tempGenMode = DistanceGenerationMode.NONE;
-						} while (tempGenMode != generationMode);
-						if (fileName != null)
-						{
-							file = new File(fileName);
-							if (file.exists())
-								break;
-						}
-						if (tempVerticalQuality == VerticalQuality.HIGH)
-							tempVerticalQuality = VerticalQuality.MEDIUM;
-						else if (tempVerticalQuality == VerticalQuality.MEDIUM)
-							tempVerticalQuality = VerticalQuality.LOW;
-					} while (tempVerticalQuality != verticalQuality);
-					if (!file.exists())
-						//there wasn't a file, don't return anything
-						continue;
+					// the file we are reading is an older version,
+					// close the reader and delete the file.
+					inputStream.close();
+					file.delete();
+					ClientApi.LOGGER.info("Outdated LOD region file for region: (" + regionX + "," + regionZ + ")"
+							+ " version found: " + fileVersion
+							+ ", version requested: " + LOD_SAVE_FILE_VERSION
+							+ ". File has been deleted.");
+					// This should not break, but be continue to see whether other detail levels can be loaded or updated
+					continue;
 				}
-				
-				
-				
-				// don't try parsing empty files
-				long dataSize = file.length();
-				dataSize -= 1;
-				if (dataSize > 0)
+				else if (fileVersion > LOD_SAVE_FILE_VERSION)
 				{
-					try (XZCompressorInputStream inputStream = new XZCompressorInputStream(new FileInputStream(file)))
-					{
-						int fileVersion;
-						fileVersion = inputStream.read();
-						
-						// check if this file can be read by this file handler
-						if (fileVersion < 6)
-						{
-							// the file we are reading is an older version,
-							// close the reader and delete the file.
-							inputStream.close();
-							file.delete();
-							ClientApi.LOGGER.info("Outdated LOD region file for region: (" + regionX + "," + regionZ + ")"
-									+ " version found: " + fileVersion
-									+ ", version requested: " + LOD_SAVE_FILE_VERSION
-									+ ". File was been deleted.");
-							// This should not break, but be continue to see whether other versions can be loaded or updated
-							continue;
-						}
-						else if (fileVersion > LOD_SAVE_FILE_VERSION)
-						{
-							// the file we are reading is a newer version,
-							// close the reader and ignore the file, we don't
-							// want to accidentally delete anything the user may want.
-							inputStream.close();
-							ClientApi.LOGGER.info("Newer LOD region file for region: (" + regionX + "," + regionZ + ")"
-									+ " version found: " + fileVersion
-									+ ", version requested: " + LOD_SAVE_FILE_VERSION
-									+ " this region will not be written to in order to protect the newer file.");
-							// This should not break, but be continue to see whether other versions can be loaded or updated
-							continue;
-						}
-						else if (fileVersion < LOD_SAVE_FILE_VERSION)
-						{
-							// this is old, but readable version
-							// read and add the data to our region
-							region.addLevelContainer(new VerticalLevelContainer(new DataInputStream(inputStream), fileVersion));
-							inputStream.close();
-						} else
-						{
-							// this file is a readable version,
-							// read and add the data to our region
-							region.addLevelContainer(new VerticalLevelContainer(new DataInputStream(inputStream), LOD_SAVE_FILE_VERSION));
-							inputStream.close();
-						}
-					}
-					catch (IOException ioEx)
-					{
-						ClientApi.LOGGER.error("LOD file read error. Unable to read to [" + fileName + "] error [" + ioEx.getMessage() + "]: ");
-						ioEx.printStackTrace();
-					}
+					// the file we are reading is a newer version,
+					// close the reader and ignore the file, we don't
+					// want to accidentally delete anything the user may want.
+					inputStream.close();
+					ClientApi.LOGGER.info("Newer LOD region file for region: (" + regionX + "," + regionZ + ")"
+							+ " version found: " + fileVersion
+							+ ", version requested: " + LOD_SAVE_FILE_VERSION
+							+ " this region will not be written to in order to protect the newer file.");
+					// This should not break, but be continue to see whether other detail levels can be loaded or updated
+					continue;
+				}
+				else if (fileVersion < LOD_SAVE_FILE_VERSION)
+				{
+					ClientApi.LOGGER.debug("Old LOD region file for region: (" + regionX + "," + regionZ + ")"
+							+ " version found: " + fileVersion
+							+ ", version requested: " + LOD_SAVE_FILE_VERSION
+							+ ". File will be loaded and updated to new format in next save.");
+					// this is old, but readable version
+					// read and add the data to our region
+					region.addLevelContainer(new VerticalLevelContainer(new DataInputStream(inputStream), fileVersion));
+					inputStream.close();
+				} else
+				{
+					// this file is a readable version,
+					// read and add the data to our region
+					region.addLevelContainer(new VerticalLevelContainer(new DataInputStream(inputStream), LOD_SAVE_FILE_VERSION));
+					inputStream.close();
 				}
 			}
-			catch (Exception e)
+			catch (IOException ioEx)
 			{
-				// the buffered reader encountered a
-				// problem reading the file
-				ClientApi.LOGGER.error("LOD file read error. Unable to read to [" + fileName + "] error [" + e.getMessage() + "]: ");
-				e.printStackTrace();
+				ClientApi.LOGGER.error("LOD file read error. Unable to read xz compressed file [" + file + "] error [" + ioEx.getMessage() + "]: ");
+				ioEx.printStackTrace();
 			}
 		}// for each detail level
 		
@@ -289,97 +232,102 @@ public class LodDimensionFileHandler
 	{
 		for (byte detailLevel = region.getMinDetailLevel(); detailLevel <= LodUtil.REGION_DETAIL_LEVEL; detailLevel++)
 		{
-			String fileName = getFileNameAndPathForRegion(region.regionPosX, region.regionPosZ, region.getGenerationMode(), detailLevel, region.getVerticalQuality());
+			// Get the old file
+			File oldFile = getRegionFile(region.regionPosX, region.regionPosZ, region.getGenerationMode(), detailLevel, region.getVerticalQuality());
+			ClientApi.LOGGER.debug("saving region [" + region.regionPosX + ", " + region.regionPosZ + "] to file.");
 			
-			// if the fileName was null that means the folder is inaccessible
-			// for some reason
-			if (fileName == null)
+			boolean isFileFullyGened = false;
+			// make sure the file and folder exists
+			if (!oldFile.exists())
 			{
-				ClientApi.LOGGER.warn("Unable to save region [" + region.regionPosX + ", " + region.regionPosZ + "] to file, file is inaccessible.");
-				return;
-			}
-			File oldFile = new File(fileName);
-			//ClientProxy.LOGGER.info("saving region [" + region.regionPosX + ", " + region.regionPosZ + "] to file.");
-			//byte[] temp = region.getLevel(detailLevel).toDataString();
-			
-			try
-			{
-				boolean isFileFullyGened = false;
-				// make sure the file and folder exists
-				if (!oldFile.exists())
-				{
-					// the file doesn't exist,
-					// create it and the folder if need be
-					if (!oldFile.getParentFile().exists())
-						oldFile.getParentFile().mkdirs();
+				// the file doesn't exist,
+				// create it and the folder if need be
+				if (!oldFile.getParentFile().exists())
+					oldFile.getParentFile().mkdirs();
+				try {
 					oldFile.createNewFile();
-				}
-				else
-				{
-					// the file exists, make sure it
-					// is the correct version.
-					// (to make sure we don't overwrite a newer
-					// version file if it exists)
-					int fileVersion = LOD_SAVE_FILE_VERSION;
-					try (XZCompressorInputStream inputStream = new XZCompressorInputStream(new FileInputStream(oldFile)))
-					{
-						fileVersion = inputStream.read();
-						inputStream.skip(1);
-						isFileFullyGened = (inputStream.read() & 0b10000000) != 0;
-						inputStream.close();
-					}
-					catch (IOException ex)
-					{
-						ex.printStackTrace();
-					}
-					
-					// check if this file can be written to by the file handler
-					if (fileVersion > LOD_SAVE_FILE_VERSION)
-					{
-						// the file we are reading is a newer version,
-						// don't write anything, we don't want to accidentally
-						// delete anything the user may want.
-						continue;
-					}
-					// if we got this far then we are good
-					// to overwrite the old file
-				}
-				// the old file is good, now create a new temporary save file
-				File newFile = new File(fileName + TMP_FILE_EXTENSION);
-				try (XZCompressorOutputStream outputStream = new XZCompressorOutputStream(new FileOutputStream(newFile), 3))
-				{
-					// add the version of this file
-					outputStream.write(LOD_SAVE_FILE_VERSION);
-					
-					// add each LodChunk to the file
-					boolean isLocalFullyGened = region.getLevel(detailLevel).writeData(new DataOutputStream(outputStream));
-					outputStream.close();
-					
-					if (!isLocalFullyGened && isFileFullyGened)
-					{
-						// existing file is complete while new one is only partially generate
-						// this can happen is for some reason loading failed
-						// this doesn't fix the bug, but at least protects old data
-						ClientApi.LOGGER.error("LOD file write error. Attempted to overwrite complete region with incomplete one [" + fileName + "]");
-						try {
-						newFile.delete();
-						} catch (SecurityException e) {
-							// Failed to delete temp file... just continue.
-						}
-						continue;
-					}
-					
-					// overwrite the old file with the new one
-					Files.move(newFile.toPath(), oldFile.toPath(), StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
-				}
-				catch (IOException ex)
-				{
-					ex.printStackTrace();
+				} catch (IOException e) {
+					ClientApi.LOGGER.error("LOD file write error. Unable to create parent directory for [" + oldFile + "] error [" + e.getMessage() + "]: ");
+					e.printStackTrace();
+					continue;
 				}
 			}
-			catch (Exception e)
+			else
 			{
-				ClientApi.LOGGER.error("LOD file write error. Unable to write to [" + fileName + "] error [" + e.getMessage() + "]: ");
+				// the file exists, make sure it
+				// is the correct version.
+				// (to make sure we don't overwrite a newer
+				// version file if it exists)
+				int fileVersion = LOD_SAVE_FILE_VERSION;
+				try (XZCompressorInputStream inputStream = new XZCompressorInputStream(new FileInputStream(oldFile)))
+				{
+					fileVersion = inputStream.read();
+					inputStream.skip(1);
+					isFileFullyGened = (inputStream.read() & 0b10000000) != 0;
+					inputStream.close();
+				}
+				catch (IOException e)
+				{
+					ClientApi.LOGGER.warn("LOD file write warning. Unable to read existing file [" + oldFile + "] version. Treating it as latest version. [" + e.getMessage() + "]: ");
+					e.printStackTrace();
+				}
+				
+				// check if this file can be written to by the file handler
+				if (fileVersion > LOD_SAVE_FILE_VERSION)
+				{
+					// the file we are reading is a newer version,
+					// don't write anything, we don't want to accidentally
+					// delete anything the user may want.
+					continue;
+				}
+				// if we got this far then we are good
+				// to overwrite the old file
+			}
+			
+			// Now create a new temporary save file
+			File tempFile;
+			try {
+				tempFile = File.createTempFile(oldFile.getName(), TMP_FILE_EXTENSION);
+			} catch (IOException e) {
+				ClientApi.LOGGER.error("LOD file write error. Unable to create temp file for [" + oldFile + "] error [" + e.getMessage() + "]: ");
+				e.printStackTrace();
+				continue;
+			}
+			tempFile.deleteOnExit(); // Mark it to be deleted on exit if any unexcepted terminations happen
+			try (XZCompressorOutputStream outputStream = new XZCompressorOutputStream(new FileOutputStream(tempFile), 3))
+			{
+				// add the version of this file
+				outputStream.write(LOD_SAVE_FILE_VERSION);
+				// add each LodChunk to the file
+				boolean isNewDataFullyGened = region.getLevel(detailLevel).writeData(new DataOutputStream(outputStream));
+				outputStream.close();
+				
+				if (!isNewDataFullyGened && isFileFullyGened)
+				{
+					// existing file is complete while new one is only partially generate
+					// this can happen is for some reason loading failed
+					// this doesn't fix the bug, but at least protects old data
+					ClientApi.LOGGER.error("LOD file write error. Attempted to overwrite complete region with incomplete one [" + oldFile + "]");
+					try {
+						tempFile.delete();
+					} catch (SecurityException e) {
+						// Failed to delete temp file... just continue.
+					}
+					continue;
+				}
+			}
+			catch (IOException e)
+			{
+				ClientApi.LOGGER.error("LOD file write error. Unable to write to temp file [" + tempFile + "] error [" + e.getMessage() + "]: ");
+				e.printStackTrace();
+				continue;
+			}
+			
+			// overwrite the old file with the new one
+			try {
+				Files.move(tempFile.toPath(), oldFile.toPath(), StandardCopyOption.ATOMIC_MOVE, StandardCopyOption.REPLACE_EXISTING);
+			} catch (IOException e) {
+				ClientApi.LOGGER.error("LOD file write error. Unable to update file [" + oldFile + "] error [" + e.getMessage() + "]: ");
 				e.printStackTrace();
 			}
 		}
@@ -398,27 +346,40 @@ public class LodDimensionFileHandler
 	 * <p>
 	 * Returns null if there is an IO or security Exception.
 	 */
-	private String getFileNameAndPathForRegion(int regionX, int regionZ, DistanceGenerationMode generationMode, byte detailLevel, VerticalQuality verticalQuality)
-	{
-		try
-		{
-			// saveFolder is something like
-			// ".\Super Flat\DIM-1\data\"
-			// or
-			// ".\Super Flat\data\"
-			return dimensionDataSaveFolder.getCanonicalPath() + File.separatorChar +
-					verticalQuality + File.separatorChar +
-					generationMode.toString() + File.separatorChar +
-					DETAIL_FOLDER_NAME_PREFIX + detailLevel + File.separatorChar +
-					FILE_NAME_PREFIX + "." + regionX + "." + regionZ + FILE_EXTENSION;
-		}
-		catch (IOException | SecurityException e)
-		{
-			ClientApi.LOGGER.warn("Unable to get the filename for the region [" + regionX + ", " + regionZ + "], error: [" + e.getMessage() + "].\n"
-					+ "One possible cause is that the process failed to read the current path location due to security config. Stacktrace: ");
-			e.printStackTrace();
-			return null;
+	
+	private String getFileBasePath() {
+		try {
+			return dimensionDataSaveFolder.getCanonicalPath() + File.separatorChar;
+		} catch (IOException e) {
+			ClientApi.LOGGER.warn("Unable to get the base save file path. One possible cause is that"
+					+ " the process failed to read the current path location due to security configs.");
+			throw new RuntimeException("DistantHorizons Get Save File Path Failure");
 		}
 	}
 	
+	private File getRegionFile(int regionX, int regionZ, DistanceGenerationMode genMode, byte detail, VerticalQuality vertQuality) {
+		return new File(getFileBasePath() + vertQuality + File.separatorChar +
+				genMode + File.separatorChar +
+				DETAIL_FOLDER_NAME_PREFIX + detail + File.separatorChar +
+				FILE_NAME_PREFIX + "." + regionX + "." + regionZ + FILE_EXTENSION);
+	}
+	
+	// Return null if no file found
+	@Nullable
+	private File getBestMatchingRegionFile(byte detailLevel, int regionX, int regionZ, DistanceGenerationMode targetGenMode, VerticalQuality targetVertQuality) {
+		DistanceGenerationMode genMode = targetGenMode;
+		// Search from least GenMode to max GenMode, than least vertQuality to max vertQuality
+		do {
+			File file = getRegionFile(regionX, regionZ, genMode, detailLevel, targetVertQuality);
+			if (file.exists()) return file; // Found target file.
+			targetGenMode = DistanceGenerationMode.next(targetGenMode);
+			if (targetGenMode == null) { // Failed to find any files for this vertQuality. Try next one up.
+				targetGenMode = genMode;
+				targetVertQuality = VerticalQuality.next(targetVertQuality);
+			}
+		} while (targetVertQuality != null);
+		return null;
+	}
+	
+	
 }
diff --git a/src/main/java/com/seibel/lod/core/util/ThreadMapUtil.java b/src/main/java/com/seibel/lod/core/util/ThreadMapUtil.java
index 9c2012f6c..5cf02a501 100644
--- a/src/main/java/com/seibel/lod/core/util/ThreadMapUtil.java
+++ b/src/main/java/com/seibel/lod/core/util/ThreadMapUtil.java
@@ -28,6 +28,8 @@ import java.util.concurrent.ConcurrentMap;
 import com.seibel.lod.core.enums.LodDirection;
 import com.seibel.lod.core.objects.VertexOptimizer;
 
+// FIXME: Nuke this whole thing and use ThreadLocal instead. And no more redundant get() please!
+
 /**
  * Holds data used by specific threads so
  * the data doesn't have to be recreated every
@@ -116,7 +118,8 @@ public class ThreadMapUtil
 	//________________________//
 	
 	
-	
+
+	//TODO: Maybe use actual valid total world height instead of always assuming the worse and alloc 1024 blocks.
 	/** returns the array filled with 0's */
 	public static long[] getBuilderVerticalArray(int detailLevel)
 	{
@@ -138,19 +141,19 @@ public class ThreadMapUtil
 	/** returns the array filled with 0's */
 	public static long[] getVerticalDataArray(int arrayLength)
 	{
-		if (!threadVerticalAddDataMap.containsKey(Thread.currentThread().getName()) || (threadVerticalAddDataMap.get(Thread.currentThread().getName()) == null))
+		long[] array = threadVerticalAddDataMap.get(Thread.currentThread().getName());
+		if (array == null || array.length != arrayLength)
 		{
-			threadVerticalAddDataMap.put(Thread.currentThread().getName(), new long[arrayLength]);
+			array = new long[arrayLength];
+			threadVerticalAddDataMap.put(Thread.currentThread().getName(), array);
 		}
 		else
-		{
-			Arrays.fill(threadVerticalAddDataMap.get(Thread.currentThread().getName()), 0);
-		}
-		return threadVerticalAddDataMap.get(Thread.currentThread().getName());
+			Arrays.fill(array, 0);
+		return array;
 	}
 	
-	
-	
+
+	//FIXME: If the arrayLength change, this may return incorrect sized array
 	/** returns the array NOT cleared every time */
 	public static short[] getHeightAndDepth(int arrayLength)
 	{
@@ -165,18 +168,19 @@ public class ThreadMapUtil
 	/** returns the array filled with 0's */
 	public static long[] getVerticalUpdateArray(int detailLevel)
 	{
-		if (!verticalUpdate.containsKey(Thread.currentThread().getName()) || (verticalUpdate.get(Thread.currentThread().getName()) == null))
+		long[][] arrays = verticalUpdate.get(Thread.currentThread().getName());
+		if (arrays == null)
 		{
-			long[][] array = new long[LodUtil.DETAIL_OPTIONS][];
-			for (int i = 1; i < LodUtil.DETAIL_OPTIONS; i++)
-				array[i] = new long[DetailDistanceUtil.getMaxVerticalData(i - 1) * 4];
-			verticalUpdate.put(Thread.currentThread().getName(), array);
+			arrays = new long[LodUtil.DETAIL_OPTIONS][];
+			verticalUpdate.put(Thread.currentThread().getName(), arrays);
 		}
+		long[] array = arrays[detailLevel];
+		int arrayLength = DetailDistanceUtil.getMaxVerticalData(detailLevel) * 4;
+		if (array == null || array.length != arrayLength)
+			array = new long[arrayLength];
 		else
-		{
-			Arrays.fill(verticalUpdate.get(Thread.currentThread().getName())[detailLevel], 0);
-		}
-		return verticalUpdate.get(Thread.currentThread().getName())[detailLevel];
+			Arrays.fill(array, 0);
+		return array;
 	}
 	
 	/** clears all arrays so they will have to be rebuilt */