Sands and gravels that possess a wide range of particle sizes with a smooth distribution of particle sizes are called "well graded" soils. If the soil particles in a sample are predominantly in a relatively narrow range of sizes, the sample is "uniformly graded". If a soil sample has distinct gaps in the gradation curve, e.g., a mixture of gravel and fine sand, with no coarse sand, the sample may be "gap graded". "Uniformly graded" and "gap graded" soils are both considered to be "poorly graded". There are many methods for measuring particle-size distribution. The two traditional methods are sieve analysis and hydrometer analysis.